Possibility and limits
This is not quite the same as the difference between pessimism and optimism. A limit-thinker might well be optimistic about how well humanity will learn to cope with its boundaries. A possibility-thinker might focus on dreadful possibilities that threaten the world. I also do not want to suggest that one sort or the other is more reliable. Limit-thinkers are often proved wrong; possibility-thinkers are often proved crazy.
So, which am I? Training in a rigorous science like physics, I think, does a couple of things. First, learning something about the laws of the physics will give you a sound appreciation of limits. Some things really are impossible. Lots of things, while not strictly impossible, are improbable enough to be effectively impossible. And some things just don't make sense. Physicists make good limit-thinkers.
But some part of me has always been wary of limit-thinkers. It seems too often that their certainties are more a product of ideology than science. Some current environmental thinking seems to be of this sort, as well as plenty of fuzzy-headed zero-sum economic views. A real knowledge of science and its history will leave you pretty convinced that (1) we have not figured it all out yet, and (2) human beings are prone to intellectual fads. Lots of things that seemed certain abou the world fifty or a hundred years ago turn out to be mistaken. We should approach our certainties with caution and humility.
(This may be why I have never really enjoyed reading Bob Park. He loves debunking, but he seems to have little discrimination -- inveighing against manned spaceflight, say, with the same sort of conviction that he criticizes cold-fusion die-hards. He is a definite limit-thinker, in my view.)
So if I had to describe myself, I would say that I am a possibility-thinker, constrained by a strong limit-thinking conscience. Or maybe I'm just flattering myself. Perhaps I should say that I am a limit-thinker with a weird streak of possibility-thinking crackpottery, which does not sound so nice. In any case, I am attracted to the idea that the world is full of surprises; and that is a big reason why I enjoyed, if only for a while, seeing 2004 MN4 touching a Torino level 4.