For me, a lot of "what if" depends upon where you make the break. I see myself as having had very little control over the bulk of my life. When I was under 21 my father controlled my life. After that control got handed over to my then-husband, who used physical force when I didn't "obey" him. Suffice it to say I'm not a "submissive" and have sworn to never wind up in that kind of situation again.
As a result, I've seen myself as someone who has had little control over her life, but has instead been reacting to whatever's been thrown at her. I wasn't allowed to apply to my first or second choice colleges. I had solid goals since my childhood, and oddly enough, I'm still pursuing them while so many of my friends have either given up on theirs or have replaced them with new ones.
I'd say most of what has affected my life were decisions made in the first 29 years by people other than me. I went out to California for the summer of '81 to see what living around my fiance would be like; instead, he blackmailed (maybe "bullied" is a better word) me into marrying him (long story). At 29 I was finally able to take back my life; since then I've been making up for lost time and lost opportunities. Sometimes I'm bitter about not getting opportunities I feel I deserve because I'm expected to "make way for younger people." When I was "younger" nobody "made way" for me; instead, I was told it was the older folks' turn, and I was supposed to wait patiently for mine.
Even leaving my husband didn't seem like a "choice," but an "either I get out or I die," which to me is not a choice. I guess I could have "chosen" not to go back and finish my degree, but I was in a situation where I couldn't get work without one (a previous recession). There were a few minor tech writing job decisions towards the end of my schooling where I basically had to choose between the job and the degree. I saw it as a "non choice," given what happened to another friend who was faced with the same decision a few years earlier who was out of work, having a hard time finding a new job, and getting lowballed. (As an aside, both companies that shafted me eventually got gobbled up by IBM.)
I saw buying my condo as a "non decision" because my potential taxes were greater than the amount of money left after the sale of the house my ex and I owned -- unless I bought property, and the place I was renting was offered to me at a bargain price. I actually did research other purchase opportunities and got discriminated against by some folks selling townhouses (they didn't have any left when I walked in, but were happy to talk to the couple who entered after me).
The one decision I've made that I'd say has affected my life was buying my house. The condo where I was living was infinitely more affordable than this house, but I was going nuts there. On one hand, it tossed out my chance of making a living in broadcasting (if I only had to pay $1500/month for my home I could perhaps survive on $40k/year). On the other hand, I'm a "house person," and moving into this place has massively improved my disposition.
I still have dreams of working full-time in broadcasting, of hosting my own TV show, and a bunch of other things. I have learned ceramics, woodworking, copper enameling (something I'd love to do again), sewing, costuming (which is beyond "just" sewing), and I've used my time in the filk community to work on the music/comedy act I've had in my head since I was a kid.
If I didn't have this house, I'd be cramped in that God-forsaken condo on one hand, but OTOH, I might have a full-time radio gig, and I wouldn't have any financial worries. Still, I'm not sure the trade-off (yes, the condo was that bad) would be worth it.