I tend to think that if I went back, if I were only armed with the information I had when I made the original decisions, I'd probably make the same ones again. I don't think any of us make lousy decisions while knowing at the time that they are lousy decisions. At least I didn't. And who knows -- maybe the opposite decision would have turned out to be even lousier than the one made.
After all, one decision, particularly a major one -- career, marriage, etc. -- isn't just one isolated decision like what to have for dinner. Major decisions have a ripple effect (i.e., the butterfly effect) which change the whole tenor of everything a person does thereafter.