I saw this quote a couple of days ago, coincidentally on the comment thread for an article -- to which I already responded, here:
"I think the reason people don't even try is because they recognize that they can't tell the difference between something that might take them 15 minutes of monkeying around to fix, and something that is beyond their competency. Worse, they are not sure that they won't make things when trying to fix the problem." (sauce)
When you think about it, it really does make sense. If time is limited, and the odds are indeterminable as to whether the task will take a non-trivial amount of time or not, most of us will err on the side of caution. The problem with erring on the side of caution, at least in my experience, is that it starts to creep in to other facets of life. You don't go up and talk to that girl/guy because you might get rejected. You play videogames because that book might be shit and you don't want to waste your time. You don't go and hang out with your friends at the bar (or wherever) because you might run into that one asshole you've always hated.
In essesence, you start to live your life as if it were constantly under threat of veto. But it isn't under threat of veto. Instead, you're staring at a deadline, because the session is ending soon whether you like it or not. And passing no legislation for fear that it might get sent back to you is a really poor excuse for someone lucky enough to occupy this office, if only briefly.