Probably the most difficult task in everyone's life. 

There's a film called "Meet Joe Black".  At the end of this film, when Bill Parrish is leaving his daughter, Susan. 

Susan)I love you, Daddy.

Bill)That's why it's okay. No regrets.

Susan)No regrets.

Bill)Its a good feeling isn't it?

We will have lived a fantastic life if we can say "no regret" without any hesitation at the end of our life, be it to ourselves or the ones we love.