It Only Moves Forward
Yes, that's probably the hardest part of life. No matter how hard you try, you just cannot go back. And you have to live with the consequences.
The corollary of this statement, is that you gain by losing. Life is like a metaphorical marketplace, you pay for what you get. Always. The experiences and wisdom can only be utilised for future; they cannot help you go back and prevent yourself from making the mistakes, that in turn, help you gained the aforementioned wisdom.
And you get to live with the knowledge that you COULD have done things differently. You COULD have ended somewhere else. You COULD have a different life. These "coulds" many a times turn into the evil imbued in one's life, always moving to ruin it. Perhaps one of the best way to live is to remember the lessons from the past, not the past itself. Forget the past as soon as you can. For life only moves forwards. You going backwards will only create friction.