What determines whether something is fun or draining? Let’s take rock climbing, for instance. If you are just running to rock climbing, having to do it, trying a few walls you might have already done, and then leaving, it’s no fun. But if you are able to lie in bed in the mornings and think about solutions you dreamed up to walls that baffled you before, see yourself doing them in your head, then you can’t wait to jump up and try them. To do this, you have to get enough sleep, because otherwise you don’t dream up the solutions, and it just becomes frustrating (this is especially important with motor skills since they are developed most in the final hours before you naturally wake up). This in turn causes you to develop bad memories with a given task, and if you are forced to continue doing it or otherwise pressured to continue doing it, you come to dislike it. That’s why I decided not to go rock climbing after I woke up from my nap and could see the incomplete begins of my solutions to the route that makes you straddle a gap on tiny footholds at the MIT rock gym — I could see it being less than maximally fun, which would give me a negative memory. If MIT students slept more, and had more freedom to leave their area of study until they naturally returned to it, maybe fewer of them would get burnt out.
I strongly refute the notion that it’s inevitable that things become less exciting as you become familiar with them. Isn’t the point of progressing forward in life to work to go up and up and up? It’s not about clinging desperately to something you are to have, but by getting better, becoming more fluent, gaining all the knowledge until you finally become too old to sustain this. Is it possible? Ask any pro-surfer. I want to become more skilled at and more in love with what I do every day, around every corner of understanding.