Søren Kierkegaard in Either/Or:

If you marry, you will regret it; if you do not marry, you will also regret it; if you marry or if you do not marry, you will regret both; whether you marry or you do not marry, you will regret both. Laugh at the world’s follies, you will regret it; weep over them, you will also regret it; if you laugh at the world’s follies or if you weep over them, you will regret both; whether you laugh at the world’s follies or you weep over them, you will regret both. Believe a girl, you will regret it; if you do not believe her, you will also regret it; if you believe a girl or you do not believe her, you will regret both; whether you believe a girl or you do not believe her, you will regret both. If you hang yourself, you will regret it; if you do not hang yourself, you will regret it; if you hang yourself or you do not hang yourself, you will regret both; whether you hang yourself or you do not hang yourself, you will regret both.

Transcending regret involves recognizing that every choice includes an opportunity cost, and learning to make peace with the myriad versions of your life that you’ve foregone or missed out on, and finding real joy in the only life you’ve got—which is the one you’re living right now.