There are several episodes in my life about which I sometimes stop and think, and wonder how things might have turned out had I chosen a different path.
In each case, the decision I made at the time was determined by the overall situation. Had the circumstances been different, I would have chosen another path.
“Ah, if I knew then what I know now…”: a futile thought. It’s currently impossible* to transmit information into the past. And if it were possible, well, that would result in a classic paradox: the new path chosen in the past (as a direct result of the additional information) would cause the present to disappear in a puff of logic — and so there would be no information to transmit to the past in the first place.
Still with me?
What’s done is done; the past is dead and gone. The future, though, that’s a different matter: the decisions we make today impact upon the lives of others; our actions spread like ripples on a pond.
Do we have free will? It’s a mystery.
* I don’t, as a rule, hold with the concept of ‘impossibility’ — until something has been tried, you don’t know what might happen.