"It is a most mortifying reflection for a man to consider what he has done, compared to what he might have done."
Samuel Johnson, 18th century English writer.
The important question is, why have you not done more than you have?
If your effort was all it could have been you should have few to no regrets.
But if you didn't do all you could, or worse, never tried, your fate is the "mortifying reflection" suggested by Mr. Johnson.