I'm a big fan of Henry David Thoreau's insights and writing. There's not much that he says that I don't agree with. But there is one quotation that is attributed to him that I do take a bit of an issue with:
"Never look back unless you are planning to go that way."
I think that advice flies in the face of ensuring that you avoid making the same mistakes in the past going forward. I also think that proper planning involves reflection and review. There are some things that you've left in the past that you never intended to leave there and if you don't look back to collect them, then you can't connect with them again and move them forward.
I think a more appropriate piece of advice is not to spend too much time looking back. I think when you do that then elements like doubt, regret, and shame can start to rear their ugly heads. It's best to look back so you can learn so that you can forge ahead with clarity and focus.