Perhaps it's a distasteful thing to say, but humans (all of us, myself included) are not particularly good at certain types of decisions, for at least a few reasons:

1) we suck at making decisions when the optimal decision requires delaying gratification.

2) some decisions are just so terribly complex (eg.: the pros and cons of vaccinations) that if you don't follow expert advice and try and build up your understanding from scratch, you're extremely unlikely to arrive at a sensible conclusion.