Sometimes it's fun to do things when there's no real world consequence attached to failure and experimentation even if the mechanics are similar to something we do for work.

I sometimes do project euler puzzles for fun. I'm a CS professor - this starts to feel kinda close to my job. But it's relaxing and there's no pressure and no one is affected when I screw up; I just get to keep kicking at it, or put it down. The freedom makes a big difference.

The "solving an interesting problem" part of my job is the part I love. It's the other stuff I need a break from sometimes. :)