I think that just depends on who you ask. I agree with /u/tannerc that I find great fulfillment in being challenged every day and working longer hours to solve problems. I find vacation tedious! If I looked back and saw that I hadn't worked as hard as I could have, I would feel nothing but regret and disappointment. I understand this isn't true for everyone, and I'm not saying it should be. But this is way I'm wired, for better or for worse.