On the other hand, a lot of this kind of wishful thinking is just so much frippery. My opinion is that most people's fundamental natures don't really change that much over time, and that much of life is inevitable. For instance, I was quite the slacker in college -- for all my impressively hugemongous SAT scores I nearly flunked out because I'd never learned to study and I was always off working on my own stuff rather than the "job" of going to class. I'd like to think that had circumstances been different I would have done better -- but then I look at my current life and realize that I haven't really changed that much (as evidenced by the fact that I'm writing this post from my cubicle at work, instead of crunching away on web code).
I still engage in the "if only X had been different" fantasy, of course. In my mind I've built up a very interesting alternate-universe version of myself, who was inspired by his helpful and not-at-all-insane parents to become a black belt by age 12 and went to Cambridge as an exchange student before getting a job at the BBC and segueing from that into a dazzling film career. And it's possible that, were I able to step through the Wayback Machine to 1978 and relive my developing years with that goal in mind, I might even pull it off.
On the other hand, it's also possible, and fairly likely, that I would get distracted and sent off-course by an entirely different set of circumstances, and end up somewhere else entirely. I nearly flunked out of Virginia Commonwealth, fer cryin' out loud ... can you imagine the spectacularly bad grades I might get at Cambridge? But of course, one of the key aspects of the fantasy is that I would have already have the hard-won lessons of how to succeed in school that enabled me to pull my VCU degree out of its tailspin and escape with a Cum Laude -- not to mention the incredibly valuable knowledge that nothing the idiots around me in high school said or did had any bearing on real life -- and thus would get spectacular grades in high school, thus getting a scholarship and being prepared to succeed brilliantly.
On the other hand, if I did have that option, that would mean throwing away the things I have actually achieved with my life so far. No laurie_robey, no Suburban Jungle, and so on. Heck, to go all George Bailey on it, no being there in the parking lot in Richmond to help those kids in the runaway car. Would I be prepared to do that? There's no way to know. But I suppose that's the great thing about it being a fantasy -- if I put my mind to it, I can think of ways to get around all those things. I mean, if you're going to dream about something, might as well shoot the works, right? :)