What matters is saying yes to the right things and no to almost everything else. Perhaps then what it is that makes the most successful people of all is the judgment (or luck) to say yes to the right things and the fortitude (or stubbornness) to say no to everything else.
"Winners never quit, and quitters never win. But people who don't win and don't quit are just stupid."
I landed on my feet. Others won't be so lucky. (Ironically, I was only able to be stubborn for so long because I had so much good fortune elsewhere. If I'd had less support, I'd have quit much earlier, and maybe it would all have turned out better.)
The moral of the story: it's better to be lucky than smart.
There's a good argument that attaining that self-knowledge takes at least a decade under any circumstances -- and if you can do so while getting a masters and PhD on the side, you've wasted less than most. :)
[1] http://www.actinginbalance.com/intelligence-is-adaptability/
If you have a lot less opportunities and far more time while starting near the bottom, a false negative can be a more significant miss for you.