It's much simpler to say "let go" than to actually do it. Consider some of the wisdom contained in the following quotations about looking back with remorse.
“Let’s dare to promote ourselves to better ‘us’ by working hard and moving forward instead of regretting and rewinding the past.” – Pantea Kalhor The advice given in this proverb is to stop dwelling on the past and make the most of the current moment.
“Stop fretting about past decisions. They have provided valuable wisdom. Go forward without fear or regret.” – Paul Martens The first quote and this one are very close. It also advises against second-guessing previous choices.
“Don’t regret your mistakes. You’ll always make mistakes. The better you are, the less mistakes you make. The only way to get better is to thoroughly analyze your mistakes.” – James Altucher
“The past could always be annihilated. Regret, denial, or forgetfulness could do that. But the future was inevitable.” – Oscar Wilde We can rewrite history, but it will still happen in the future.
“One of the greatest regrets in life is being what others would want you to be, rather than being yourself.” – Shannon L. Alder We shouldn't try to be what other people want us to be, but rather who we really are.
“Embrace the glorious mess that you are.” — Elizabeth Gilbert It is counterproductive to judge oneself by the standards of those who appear more competent than oneself.
Regret is an odd emotion because it comes only upon reflection. Regret lacks immediacy, and so its power seldom influences events when it could do some good.” – William O’Rourke
“In history as in human life, regret does not bring back a lost moment, and a thousand years will not recover something lost in a single hour.” – Stefan Zweig
“Sure, you wish you did some things differently. But there is no sense in becoming burdened with regret over things you have no power to change.” – Rihanna
“We don’t have to be defined by the things we did or didn’t do in our past. Some people allow themselves to be controlled by regret. Maybe it’s a regret, maybe it’s not. It’s merely something that happened. Get over it.” – Pittacus Lore