Some people really like the concept of at-will employment where anyone can be fired with no notice, for no reason given. You have to earn your job on a daily basis, and live up to it. There's no security or relaxation. You never keep a job when someone else wants it and has more merit.
Except this is mitigated by transaction costs – if you underperform by $5, but switching employees costs $500, then you can keep your job. Transaction costs keep things a little bit more stable, but really don't offer much security in most cases. Transaction costs are logical because if everyone was changing jobs every day it'd be chaotic and waste a lot of effort on retraining. They don't mess up the principle.
The principle involves interacting on a case-by-case basis, for mutual benefit each time. If the mutual benefit ever stops, the interaction stops. If someone can get a better deal elsewhere, they should do that (make sure to factor in the price of making a change, which includes researching alternative options, the risk the new one doesn't work as well as you predict, turning off any old recurring stuff, setting things up with the new guy, etc).
Other people less into freedom, capitalism, voluntary win/win interactions, economic literacy, reason, Objectivism, etc, have a different approach to employment. They want regulations to create job security. They want it to be hard to fire a person without giving a good reason. They want predictability and security, so people can relax once they get a job (they can't just do a terrible job, but they can relax and do a pretty good job and not worry about it). They want unemployment insurance/welfare and to make sure everyone has a stable job they can build a life around.
Some people prefer to be able to start and stop jobs easily, others prefer to just get a job and keep it. Both of those preferences are OK. What's not OK is regulations to make it hard to fire people and to protect their jobs even if the employer no longer considers it mutually beneficial to keep them. What's not OK is a ton of paperwork when you want to hire someone to increase the transaction costs of getting a new employee, to artificially reduce (via government policy, something built into the logic of reality) the frequency that people get replaced at a job.
If you want a stable longterm job, why not get a contract? Why not write in the contract that you're guaranteed to keep the job for 20 years as long as you meet some minimum conditions (specified in the contract), and if they want to fire you, they either have to have a good reason (specified in the contract, e.g. they went out of business) or else they have to pay you money to make up for it.
Of course such a contract would be very expensive. Who wants to commit to keep an employee long term and make it hard to replace them?
Categorize all scenarios into two groups. There are the scenarios where a person staying at a job has mutual benefit, and where it doesn't. For the first category, they are going to keep the job without any contract or regulations protecting them. But for the second category, they will only keep the job if there is a contract or regulations or something to protect their job security. The entire purpose of this sort of regulation that limits at-will employment is to keep people in jobs where there isn't mutual benefit. If you want a contract where the employer agrees that in some potential future scenarios, they will keep paying you money in a way they don't benefit from, then that's going to be very expensive. They would have to pay you a lot less, so they benefit so much most of the time to make up for the risk.
And what if, knowing it's hard to fire you, you don't do your best work? Why would anyone want to sign a contract setting it up for an employee to do that and get away with it? Well the government regulations work similarly. Those regulations lower wages, they encourage companies to have fewer employees and to be less willing to take a risk on someone they aren't really confident about (which especially hurts younger people without a long track record).
OK, now you've got a refresher on free employment – firing someone at any time without giving a reason – and regulated employment to create job security so people don't have to constantly strive to have the most merit.
Application To RelationshipsMost long term relationships follow the job security model. (Most casual hookups follow the at-will employment model.) In particular, marriage tries to set up job security so you don't have to compete with everyone else your spouse might like better all the time.
The idea is you can relax and be secure in your marriage instead of constantly worrying about dog-eat-dog competition. You can have a stable situation to build a life around, at the cost of sometimes you have to sacrifice – do stuff that lacks mutual benefit, give up things you'd prefer instead. (Your spouse makes the equivalent sacrifice. You both sacrifice alternatives you regard as superior to the spouse. But also you lie that the spouse is the best, and you change your mindset to not look for alternatives and not think about whether alternatives are superior, to try to hide the sacrifice from yourself.)
Job security marriages are bad like job security regulations. Relationships should be merit and mutual benefit based, at all times, just like employment should be. If you want stability, figure out a rational contract that makes sense. If you can't do that, maybe it's because you're trying to make the future predictable in ways the future isn't predictable – so you have to sacrifice big things like the growth of knowledge to artificially create more predictability.
Marriage and job security encourage taking things for granted and coasting through life. And even if you're not married, having "the talk" and being officially "boyfriend and girlfriend" can also put things into that same mode where all the inertia is in favor of continuing on, and there's a lot of pressure to prevent changes. When you make relationship commitments that make change hard and artificially add extra cost to making a change, then that's irrationally propping up something that wouldn't work on merit alone.