Reasonable exercise.
If you're going crazy and overexerting yourself, yeah I think that puts a lot of people off exercising at all because you're doing more than your current level of fitness can handle, but once you start doing regular low-impact exercise appropriate to your level of fitness like walking or swimming you realise you feel so much better doing it and so much worse/less energetic when you don't for a day.
I'm going through this realisation right now.