This is adapted from a Fallible Ideas discussion called "How to help someone find their motor".
How do you tell the difference between genuine vs. cargo culting interests? You don’t give up / lose interest in a genuine interest just because it gets hard or when some passing
distraction comes up and catches your attention.
that describes a big, strong* interest.
lots of interests are genuine but small and/or weak.
it's good to have lots of small interests where you finish quickly. you should have more small interests than big ones. that's part of creating lots of interests. not everything has to be or should be a giant quest.
and it's fine to have lots of weak interests where, if you realize the price is higher than you initially estimated, you drop the project. that's efficient. most of your interests should be sensitive to the time/effort/money/resources involved in a project. you can have a few things where you're like "whatever it takes, i wanna do this" but you shouldn't have that attitude all the time (also you should always be willing to reconsider goals, change interests, etc). it often makes sense to have some weak interest in 20 projects and then actually do the 3 you find to be most cost efficient and drop the other 17. (don't lose track of what you actually like looking for what's cost efficient, though! use cost efficient as a tiebreaker between different things you like about equally.)
small projects often lead to new problems and projects, which are often small themselves, and lead to even more.
people should be interested in problems more than topics. topics are only an approximation of rational interests. super dedicated chess players don't actually like everything about chess, they are more interested in some aspects than others. some chess problems interest them and some don't. saying they are interested in the topic of chess is a reasonable approximation because they are interested in a wide variety and large number of chess problems.
even a very broad problem like being interested in winning chess games is more of a specific problem than chess as a topic. winning chess games covers a lot of material, but chess as a topic includes even more stuff that doesn't actually help you win games.
looking at it abstractly, out of all possible information related to chess in some way, most is not useful to any problem a human cares about. most information about all topics is boring. selecting interesting problems to guide you is crucial to making good decisions about which information to focus on and which to ignore.
anyway, one doesn't just sit down and "study chess". that's either an approximate statement (no big deal normally, but imprecise) or wrong. one studies a chess related problem, e.g. on a particular day one sits down and studies how to win games against the Najdorf variation of the Sicilian defense, which fits into one's broader interest of being prepared to play aggressive e4 openings in order to win rather than draw more games with white and play to one's strengths of fast, open positions. which will help solve the problem of winning chess tournaments, not the problem of knowing every fact, no matter how pointless, about chess just b/c "i'm interested in chess" (no you're not, you're interested in lots of chess stuff, but not all of it!). people often do this is a semi-reasonable way in practice, but don't understand it in words very well, and could make some improvements if they knew what was going on more accurately.
so: find projects to solve problems, preferably usually small ones you can finish. do them successfully. do more. don't look for a whole huge quest from the start if you don't have one. bigger projects may develop naturally as you do lots of small projects successfully and develop various skills and gradually increase the size of project you can confidently complete and handle. those skills include time organization and resource management skills, understanding your interests and what you'll actually do or finish, general purpose get-shit-done skills, and much more.
it's better if small problems you work on relate to a larger interest, even if it's one you're unsure about. e.g. you might find a chess opening interesting to learn about on its own, and it'd also have the additional big-picture benefit of helping your chess game. or if you think you might potentially like to learn some physics stuff, then you could look for little projects with some connection to physics. like anything to do with science, learning, writing or computer skills could come in handy later for learning physics.
What if my interest leads to a dead end?
suppose theoretically you did follow an interest to a dead-end. dead-ends are bad so that means you made a mistake. that leads somewhere: you could investigate why you made that mistake, what went wrong, how to find, fix and avoid mistakes in the future, what kinds of methods and ideas that requires, what errors and error correction are, etc... so it's led to lots of great stuff. so it wasn't actually a dead-end in the bigger picture.
broadly: solutions lead to new problems. in the alternative, lack of solutions is a problem. there's always more problems to work on. there are no dead ends except irrationality (which shouldn't be blamed on the interest/topic, irrationality is about how people approach stuff badly and e.g. create dead ends).