Not what you did. Who you didn't become.

When Cornell psychologists asked people for their biggest life regret, 76% named failing to become their ideal self — far more than failing at duties. Co-author Gilovich put it this way: a should-regret is a puddle on the road, a problem now behind you; an ideal-regret is what you see through the windshield for the rest of your life. At forty he left the accounting firm and started drawing again, the thing he had wanted at twenty. Late, but nothing on the windshield disappears.