In addition to mental stamina and things like wife and kids taking lots of time, which others mentioned and I heartily agree with, there's also a gain of confid

In addition to mental stamina and things like wife and kids taking lots of time, which others mentioned and I heartily agree with, there's also a gain of confidence. When I was young, if some management type had told me we were going to miss a deadline I would've pulled all nighters, worked weekends, whatever it took to help bring the deliverable in in time. Nowadays (at least before I stopped working) I would just say something like "Okay, let me know when we have an updated schedule." Before, when my manager had said we need to work weekends, I'd be there. Now, I'd just say that I'm not doing that. The confidence comes from experience, knowing that I could get a different job, being financially secure, and a self confidence that I didn't possess in my youth.