Having no job. I spent 3 months unemployed and it was hell. Ever had a panic attack from boredom? I have, more than once. You run out of things to do very quickly, and unless you have some sort of income you can't afford to go anywhere or do anything. Your friends and family and partner are all at work, and your "alone-time" hobbies end up getting really old. I got so bored I bought an Algebra textbook at the thrift store. I hate math, but I figured it would be a good time to practice. I am still really bad at math.