I have been an assistant professor for one year now. And thinking about it today, I realize it's a lot easier than being a grad student.
True, I work a lot harder than I did as a post-doc, and that involved working harder than grad school. I do of course accomplish a lot more daily. There is definitely more stress and anxiety - more people depend on me, and the amount of time I have to succeed seems shorter. As a professor the number of different skills I am called on to use is greater, and the deadlines are shorter. I work more hours more consistently, and I have watched a lot less television (still a couple seasons behind on Fringe).
But given all that, it's easier being a professor.
The reason is, I now have confidence that I can do it.
When I was a grad student, I had no guarantee that I would ever be good at science. I wasn't sure my work would pay off so it was harder to do. I was at the bottom of the learning curve and every step was new and different.
Even the new things, if I fail at them, I still have the other things to count on as backup. I didn't have that in grad school. I just had a college diploma. And it was like that thru most of grad school. I didn't get any publications until right before I graduated, and I didn't even do an SFN poster until 4 years in. I was off in the wilderness and I had no external validation from the field. I was on the outside looking in, and there was no clear way in. That's a really hard and draining place to me.
Based on my own experiences, I do think that confidence in one's ability to achieve one's goals (known to social psychologists as self-efficacy) is one of the biggest factors in determining motivation. And motivation can determine success.
If I believe my grant may be funded, I will work on it until 2 am; if I believe it's a crapshoot, I'll submit a half-baked one. If I believe it probably won't be funded, I'll spend the afternoon reading slate.com.
I gained a big boost when I got my Ph.D. Then I really felt like "no matter what, they can't take this from me." When I got a couple publications, I could look back and say, those are in the scientific literature forever.
I try to remember this in my mentoring. I try to give more sympathy for the students than I would be inclined to. I think it might make the difference. I know for me back in the day having an advisor who could provide some validation kept me going through the roughest spots.