That's right along the line of what if I had entered the right lottery numbers or bought Apple when it was low. You can regret any decision you make in life with hindsight.
If I am feeling down about not joining YC 15 years back, and someone says 'why don't you feel bad about not buying bitcoin 5 years back, or GOOG 20 years back, or AAPL 40 years back, or X Y years back', I'll soon realize a pattern that I can feel sad about ANYTHING if I put my mind to it
And since it's our natural state to feel happy, and not feel sad, above knowledge might stop me from acting 'human' (depressed) over inevitable/infinite things.