From what I've seen, people who don't expect to amount to much typically don't. People who expect things to go badly for them are often right.

I wonder if it is self-manifestation, or just reality settling in?

I think you need both. Both to give it your best, and to expect best. Or at least, as you said, better.

I used to be an optimist, thinking things would work out, no matter how bad conditions were. I feel I have lost it over the years, so while I work hard, I am not sure I expect it to work, if that makes sense.