> It's not what you are, it's what you don't become that hurts.

(Oscar Levant, pianist, composer, author, comedian, and actor)

> Regret for the things we did can be tempered by time; it is regret for the things we did not do that is inconsolable.  

(Sydney J. Harris, journalist)

> Maybe all one can do is hope to end up with the right regrets.

Arthur Miller (playwright)

> A man is not old until regrets take the place of dreams.

John Barrymore (actor)

> For of all sad words of tongue or pen, The saddest are these: 'It might have been!

John Greenleaf Whittier (poet and abolitionist)

> Every man is guilty of all the good he didn't do.

Voltaire (author)

> I regret that it takes a life to learn how to live.     

Jonathan Safran Foer

> Regrets are the natural property of grey hairs.     

Charles Dickens 

> A man is not old until his regrets take the place of his dreams.

Yiddish proverb

> The first half of life is spent in longing for the second, the second half in regretting the first.

French Proverb

> One doesn’t recognize the really important moments in one’s life until it’s too late.

Agatha Christie

Does any of these suit?


How did I find these?  I googled 

> regrets proverb

As you can see, I got a pretty good harvest.  But some of the phrases that turned up were totally useless.  Best example of this: "I regret to say that we of the F.B.I. are powerless to act in cases of oral-genital intimacy, unless it has in some way obstructed interstate commerce." -- J. Edgar Hoover