According to Albert Einstein, insanity is doing the same thing over and over again and expecting different results.
This is probably why most great people are at least a bit insane.
Alex Hormozi said that extraordinary accomplishments come from doing ordinary things for extraordinary periods of time, which is true. But take that a few steps further - most great people have banged their head against a particular problem, field of work or goal for an insanely long amount of time, and have thus produced extraordinary results.
(Note: you can substitute "expertise" in a "field" for "progress" towards a "goal" or any such synonym for progress towards greatness in a paradigm)
There was probably a time where you could become a "great person" in a field with a relatively minimal effort because the field was extremely niche and didn't have a lot of people actively trying to get better at it. There probably still are fields that you could get stupidly good at relative to other humans with relatively minimal amount of effort (compared to the effort needed to become world-class at other, more mainstream activities), but what's the use of that? Since greatness is a function of how great you are in a particular field and the greatness of that field, being great in an irrelevant field and being irrelevant in a great field are both useless.
Again, let me reiterate that this is assuming that your goal is do great things and that you are stupidly ambitious. If you wish to collect peak experiences and the outcome isn't as much of a priority for you, sure, please do what makes you happy! The lives of people striving to improve human experience are meaningless without lives of people actually experiencing.
But I digress.
The point I was trying to make is that nowadays, in order to be great, you need to put in insane amounts of effort in one particular field, or towards a particular goal. In other words, your life must be strictly bounded. I am aware that these two are not exactly synonymous, since progress towards a goal might require dabbling in multiple fields, but I am assuming that you, the reader, possess enough goodwill not to strawman my argument.
And since "putting in ungodly amounts of effort" simply looks like repetition in practice, the path towards being great (waking up and focusing your efforts on the same problem for insanely long periods of time) and path towards insanity (waking up and doing the same thing over and over again) are eerily similar. Maybe even the same thing altogether.
If I want to learn how to code, I will have to wake up everyday and work through a bunch of material, implement it, reflect, repeat. I will have to do this for a very long time to get any good at coding.
In the process of writing this essay I have now realized that I have been operating off of a flawed definition of insanity. I focused on the "doing the same thing over and over again" part and not so much on the "expecting different results part".
This raises an interesting question though. It's not "how and why great people are insane" but "if both great people and insane people do the same thing over and over again, what's different about great people?"
Obviously, it would have to be something to do with expectations. Either that or there's some flaw in my definition of repetition.
I'm pretty sure it's the second one. When I refer to "repetition" I refer to the general structure of the activity itself, like going to the lab or sitting down and coding. The actual content of the activity can and should differ wildly. Oh. Then are great people not doing the same thing over and over again? That doesn't sound right to me.
Okay scratch the content of the activity should differ claim.
I think I have it. I think it's a matter of the relation between activity and the goal. Great people are intentional - they have a goal and their repetition is in service of that goal. Either that or they're so passionate about what they're doing that their repetition is an afterthought. Both ways the action serves a purpose - either to get closer to a pre-defined goal, or to provide satisfaction in and of itself.
Insane people, on the other hand, repeat actions without a clearly predefined outcome or passion.
Update: I think I have it. Great people are either divorced from expectations, having no expectations at all (in the case of passion driven work) or have a good grasp of how their current actions will lead towards their goal. Insane people, on the other hand, are both attached to the outcome and have no way of gauging how changing the current action will change the outcome, thus their repetition is simply the only way they know how to get closer to the goal. Repetition in insane people is a side effect, repetition in great people is intentional.