I think is fear.
It's only natural, of course, living in the USA, because our government currently gets us to agree to do things by tapping into our fear. But I'm talking about something more personal. And, it may not really be "fear" as much as "worry". The whole "what if" thing.
At the most base level, it's probably the same "what if" so many people share, and some people much more directly than myself. "What if I lose my job?" Then I can't pay for the house. I can't pay for health insurance, which my wife and I need (literally in my wife's case) to survive. I know that the stress of that situation would be killer. I lived for a few years in academia with the near-certain knowledge that I was going to lose my job, and knew the time when it would happen.
Nowadays, I like my job, I like the people I'm working with, I like the day-by-day work of it. I'm a happier person. But underneath all of that is my fear. And, when I see something, or do something stupid, that makes me think that the worry underneath perhaps isn't as completely irrational as it usually is, it gets very hard, at least for a short period of time, to carry on like a rational human being.
Worrying about the future has always been a week point for me. Before my academia-induced depression turned to basic out-and-out despair, it usually manifested itself as worrying, worrying that would take over my brain and freeze me up from being able to do other things. It still comes back sometimes. And then I kick myself for having done the stupid thing that led me to think that perhaps I really had something to worry about, or for blowing something that I observed out of proportion.
It is kind of sad, though, that all of us in our society, in or out of academia, spend our lives in fear that we have to hang on to whatever income-earning activies we have or else we're going to be in trouble, unable to meet our responsibilities, unable to survive. That at the base there isn't a drive to make the world a better place, an appreciation of beauty, a wonderful curiosity, but rather simple personal fear that the bottom is going to drop out and we're going to be in trouble. No wonder we're such an on-the-edge society!
Although, truth to tell, I suspect it was worse through most of human history.
All very sad.