Doing something that’s fun and hard.

If it was easy, it wouldn't be any fun.

I have to say this to my all the time to my friend who got into Harvard from across the pond who seems to deliberately pick "easy" courses with lots of book work and therefore burns out e.g. if you want to learn complex analysis, the hard course that requires thinking will probably have less tedious homework to do for example.

It's the same with competition. Who wants to enter a competition that's an easy win? There's no joy in that. Far more fun competing with people who are very good.

Must be fun!