There are 365 days in a year.
You likely work for approximately 250 of them.
Of those days, 8 hours of each day will be sleep. 8 hours will be work. 2 hours likely represents the time you commute/get ready for work/get ready for bed, and 2 hours to keep up on chores and get/eat food. Thus you should have around 3 hours to yourself each working day to do things you want to do. During your work week, you have a total of 750 hours. I will leave the 1248 hours you get from weekends alone plus around 10 holidays for the purposes of this, which will involve a lot of unwinding and recreation.
You could spend those 3 hours as a zombie, watching TV, masturbating, and browsing internet memes all day to unwind from your mentally draining existence. But I propose something different.
It takes approximately 300 hours to become reasonably proficient in most skills. Every year, you can learn to be good at 2-3 new things that you couldn't do before with just the time allotted here. You don't even need to use the full time to get two under your belt. These skills could be almost anything you want and are interested in. With this time and some discipline, you could easily dedicate yourself to be a true renaissance man.
Or you could pick up a very practical, but fun skill, like cooking, gardening, woodworking, metalworking, tiling, plumbing, or electronics. With a practical skill like cooking or gardening, you can even easily integrate your learning time into your routine.
Society wants you to be specialized: more or less, you are expected to be very good at your job, and to just do that very well while more or less spending the rest of your money on the work of other specialists and hoping compound interest will bail out your lack of frugality. You could in fact, go along with this, and use your 750 hours to become a god of your craft, or to squeeze in a side gig of your current specialty to try and get a little debt paydown money. But I would argue, this is the least good route to take if you are in a stable position because the best you can hope for with this is just more money. That will only get you so far.
The end result of this line of thinking – if a man were to follow the conventional line of advice: work on your specialty, save a pittance, pay everyone do to everything else – is a man living in virtual indentured servitude in an apartment, entirely dependent on the work of others to make so much as spaghetti, working forever in a job he never wanted doing things he never cared about. After decades of service, when he is useless and the project he dedicated his time to is derelict after the next big thing wiped it away anyway, he will be tossed aside like a used-up kitchen sponge. After aimlessly wandering about on ever dwindling amount of funds, unable to do what he wanted because he patiently waited to do them in a decrepit body with a failing mind, he dies penniless, senile and drooling on a nursing home cot. There, he will be preserved and buried in a hermetically sealed sarcophagus, as another curious artifact of modern times. Perhaps, many centuries in the future some intelligent cockroach will find and unseal him and his colleagues to study them within their completely toxic burial ground: a man who by some faded data in a dusty mainframe somewhere should have existed, but never really lived at all. A successful, mass produced, intentionally molded failure.
Dedicating your 2-3 new skills to be matters entirely new, particularly the practical skills, will ultimately do you better. By doing this you are developing something of much greater value than anything else: self-sufficiency, and future-proofing.
Every specialty that you can do by yourself on a practical level is a large expense that you can avert. That's a plumbing disaster that you'll be able to clear up. That's a new and better light fixture you can install yourself. That's a broken computer that can run for another several years. That's a bitching new house-on-wheels that you designed and created yourself. That's food which you yourself could cultivate. When life hits you with things you don't expect, you can be ready to tackle it. When you need things you otherwise have no access to, you can be the one to do it. You might not be the absolute best at any of those things, but that's okay. Just by learning them, you have given yourself an incredible amount of power and freedom. When you want to make it your goal to stop working early, these things will save you – and with enough under your belt – allow you to live wherever you need to or want to, independently of your job income.
It also means that you are in a position where you can do things that many, many other people have resigned themselves as entirely incapable of doing. If your one true job gets automated away, or outmoded, or society starts to crack to the point that your highly specialized job can't be justified anymore, that doesn't matter, because you can do at least 3 other things people around you desperately need. And if things get really bad, besides some downshifting, you won't have to care at all. With ingenuity, you'll be able to be your own master, and head out to do other things in other places entirely.
That's not to mention that picking up and learning a new skill is overall a fun and enjoyable process. Especially when it's not something you already do. It breaks things up a little while enriching you at the same time. You don't have to learn everything linearly either; there's no reason you can't improve upon, say, 5 things which you have to do often over the course of 2 years rather than just 2 things over 1 year. The point is, to make yourself a better and more independent person, and have fun doing it.
What are your skills going to be?