Sometimes it's a character you want to play or a story you want to tell. Sometimes it's just to pay the bills.
“Too much coffee. Too much coffee and Gatorade. It's a hell of a mix. If you're ever tired in the morning, just try that mix, and tell me what you think.”
“It is no good getting furious if you get stuck. What I do is keep thinking about the problem but work on something else. Sometimes it is years before I see the way forward. In the case of information loss and black holes, it was 29 years.”