I think the meaning of hard/easy used in the statement is the second one, i.e. hard/easy for me (now). Whether or not something is also considered inherently hard doesn’t matter. The key is whether it’s currently hard for you — whether your manager is going to have to do it.
It’s still unclear to me whether “only do things which are easy" is suggesting that people not try to fix irrational thinking methods or figure out how to use FI if they consider those things to be hard.
there is a learning/doing distinction. first you learn how to do something, say dentistry, then you do it (fill cavities, etc). so one of the meanings is you should learn enough that dentistry is easy before it's your job. don't learn enough you can do it, learn enough that it is now easy. dentists should have mastery so they can do it with a low error rate (and VERY LOW rate of major errors) even when tired, distracted, unfocused, etc.
and also the learning process shouldn't really be hard. say you're trying to beat a level in a video game. if your goal is "beat the level" then that's hard. but that's about doing, not learning. if your goal is "try strategy X and see if it works or not", that could be a step towards learning to beat the level which is also easy. if strategy X is too hard, then you could have easy immediate goals like "try action X1" and "try action X2" and so on – try out individual parts of it before trying to do the whole thing.
in Vindictus (example gameplay video) there are lots of boss fights you can do by yourself and get a gold medal for being hit 3 times or fewer. success is hard in some sense. but the learning process doesn't have to involve hard steps. first you can just stand there and let the boss hit you and watch what he does. that's easy! after you watch a bit, you can start to figure out what his attacks are. lots of the bosses only have like 5 different attacks. if remembering is hard you can write them down. you can even record video clips of each attack. that's more work but it isn't hard. so this step of seeing what the attacks are can be pretty easy, especially if you aren't rushing yourself. like if you are trying to remember every attack after you've seen it once, that's hard. but if you take your time and are OK with remembering an attack after seeing it 10 times, then it's not very hard.
the next step is blocking/dodging attacks (each character in the game has a few defensive options, mostly dodges and blocks). you can figure this out without doing anything hard, too. for each boss attack, try your first defensive move at various different timings. you can get a good idea of the right timing by letting the boss hit you and seeing what you take damage. your defensive move should generally be used around .5 seconds before the time you took damage, though it varies by move. if this isn't working well, try your character's second and third defensive moves and see if they work better for dealing with this attack.
many boss attacks have multiple parts. like they swing their sword 3 times in a row, and it's a set pattern of those 3 swings. so you can figure out a series of 2-3 defensive moves to defend against all 3 sword swings. (sometimes attacks come close together and you can stop multiple attacks with one defense.)
for each attack, there is some kind of clue that it's coming. the main clues are animations like a boss moves his sword or shoulders back before swinging forward. you see them getting ready to attack in some way. so you also need to learn some kinda thing that you will react to – the signal that it's time to do that defensive pattern for that move.
this can all be done pretty intuitively but it can also be done by conscious design and you write a list of every attack, every signal its coming, and what defensive moves you plan to use for that attack.
which part of that is hard? no part. if you do it in this methodical way, every part is easy. it's not like you need super fast reactions times. the game isn't hard in that way. if you calmly watch for the signal that a specific attack is coming, and you aren't worrying about anything else, then you can block/dodge it with a bit of practice, it's not that hard (and if a different attack happens first you just let it hit you and wait until the boss does the one you're trying to stop).
the individual parts of the game aren't that hard. but the complexity adds up when you're watching for 10 different possible attacks (on the harder, more complicated bosses) while also doing your attacks and also there are other allies on your team who the boss might target (if the boss does a move aimed at you, or aimed at a guy off to your right, then the patterns of blocks and dodges that protect you, and the timing to do them, can be different. where the boss is aiming changes where his sword ends up at different times.) and also you can be remembering to drink health potions every 4 seconds and use your cat statue every 70 seconds and tracking how much SP you have (points for doing special moves) and then managing which special moves to use, when, and so on. and then your ally dies and you want to go resurrect him but that requires standing still for 3 seconds so you have to find a safe time to do that between boss attacks. etc.
but basically all of that can be learned as a sequence of easy steps, too.
once you learn to defend attacks you practice until it becomes more of an automatic habit. you get it to the point its easy to do all the attacks for a boss, it's second nature, its intuitive, your error rate is low. then you try attacking in between the bosses attacks. you'll already have a sense of how much downtime there is after which attacks since you've seen them a bunch. so you can estimate how big of an attack you can fit in after each boss attack, and you try it out and see what works. that's assuming you can already do your attacks easily. if you can't, no problem, you just practice attacking without worrying about defense (initially just do this in an empty area with no enemies). and then practice on easy enemies where getting hit isn't a big deal, so even if your error rate for defense is high, cuz you're focused on attacking, it doesn't matter much.
before you actually use your attacking or defending as a skill – before you try to DO it for real instead of doing it in a learning/practicing context – you need to get it to be easy, you master it so an automatic mental workstation can do it. so by the time you're trying to kill the boss, you have all the skills needed to do it, and it isn't scary or hard like it would be if you just went up to him the first time and tried to win.
and after you practice, you still don't expect to win. if your goal was to go straight from practice to success then that'd be hard. instead, you practice and then you try fighting the boss for real as a test to see how well you do. you're checking how effective your practice was, what your error rate currently is. that's easy cuz the goal isn't "make no errors", the goal is "see how many errors i make". so you do the blocking and attacking in easy, automated ways, which is important cuz now your conscious attention is mostly used for just watching to see how often you screw up. that's not a hard thing to do! you just autopilot attacking and defending while consciously watching how well it works. that's it. ez. then you can see if you need more practice, and if so for which parts. and you can also identify problems like a particular strategy for blocking a particular move is unreliable, so maybe you need more practice or maybe you need to change the strategy – do a different defensive option or do the first block after an earlier visual cue. there are other errors you'll see happen, like a boss can have two different attacks that look similar at first, so you mix them up and sometimes you do the defense for attack 1 when the boss is doing attack 2, so it doesn't work. so while you're autopiloting and seeing how it goes, you can watch for issues like that with your conscious attention, and then you can figure out a solution, like you can look at the attacks more closely until you find a difference which is pretty easy for you to recognize once you know what to look for, and then you can start looking for that and, with a little practice, autopilot doing that. or you can also find a defensive option that works for the first part of both attacks, so it's ok if you don't know which is which until you're doing the second defensive move.
people find the game hard cuz they are trying to e.g. do lots of attacking right now instead of just focusing their attention on defense. or they never practice alone, they just fight in groups where other people are always moving the boss around and creating chaos, and everyone is rushing to keep up with everyone else on doing damage. and if you are just less ambitious in the short term, you can make tons of stuff way easier. i was having trouble with some bosses in the last two days and what i started doing is only using my simplest attack which takes the shortest time. that immediately solved the problem of doing an attack that is too long and then i'm not ready to defend against the boss's next attack. and it meant attacking took even less attention and i could focus on defense more. the downside is that the simplest, fastest attack does the lowest damage. but so what? a bit of patience made it way easier and actually saved time overall (cuz it takes longer to kill the boss, but fewer retries, so actually that saves time). that works great on bosses where my goal is to get the gold medal one time – if it's 5 minutes slower but saves some retries that's fine. i don't need efficient offense for a boss where i just want one good kill. there are other bosses that you fight more often so you want to learn to do your offense more efficiently, but it's not needed in all cases. (also part of the issue is some of the old bosses i was fighting, which i only needed one good kill on, actually have different designs than some of the modern bosses that people fight more. some of them actually have overly short windows for you to attack during if you are playing alone. it's fine if you play with an ally cuz then half the time the boss attacks the ally and you can just go stand behind the boss and have time to attack. but for certain heroes, soloing some of the old bosses involves shorter attack windows than you're used to with the modern bosses, so partly you just need to be willing to use your small attacks and be content with that. and if you had to fight that boss every day it'd be annoying, but you don't, and the newer bosses you fight more often have some larger downtime parts built in, on purpose, to let you do your big attacks sometimes.)
the point of this example is if you approach things step by step, every step can be easy. cuz you have a specific goal in the current step which is not big picture success, and you just do that.