It occurred to me a while ago that you should never regret the past if you are the slightest bit happy with who or where or what you are because the events of your past all had to happen to get you to who or what or where you are now, so if there is anything about your life you are happy about, then your past was necessary and you can stop regretting it but rather cherishing it; and if there isn’t anything you like about your life then I think you would be far better off fixing the present than worrying about the past. There is a popular idea of one of the perils of time travel, if we were ever to invent it, called the Butterfly Effect, the idea of which is that any tiny event has ever growing effects like dominos spreading out through time, the classic example being that if a butterfly flaps its wings in one country it can cause slight pressure changes in the air which will slightly alter the path of a gust of wind which will change where that gust of wind will end up, and so on and so on until across the ocean a hurricane is formed which would not have happened without the butterfly, so if you were to travel back in time and accidently step on that butterfly, you would change the course of history. The Butterfly effect is a quaint little illustration of how every tiny action has huge consequences, meaning everything, even the bad, was important. Just to take a few examples from my life: 1) I was bulled at school quite badly, but I don’t regret it because it gave me a strength that I am proud of, because of this I do not hold any ill will towards the bullies. 2) I was clinically depressed at university, it screwed up my degree and was responsible for the worst 3-4 years of my life, I came so close to killing myself, but I value that experience because it has not only given me the knowledge I need to prevent it happening again, but gave me the tools I needed to help my sister when she was depressed, and I think feeling that misery made me a softer and kinder person. 3) My first girlfriend, I was a horny teen and I treated her like a sex object, it was wrong and I was a shameful boyfriend, but after a series of bad boyfriends she ended up with a good guy and is very happy and I learned a valuable lesson too, I was not ready to be a boyfriend, and I also know how important it is to treat women properly in a relationship now, that shame thinking about how I acted will make sure that when I do meet the right girl, she will be treated as she deserves. This list goes on and on, some are bad things that happened to me, others are bad things I did which I used to regret, but think about this, if you went back and changed it all, got rid of the bad times, you would lose everything you learned and everything it made you, pain and failure is more important than success because success makes you happy but failure lets you learn and evolve. If you undid all the things you regret you would lose many of the best parts of yourself, including the parts of yourself which knows to make sure those things don’t happen again. So, short version, if you could undo your past, but lose everything in you that you learned from those experiences, every bit of patience and strength and dignity, would it be worth it? Personally, even though I am on anti-depressants as I type this, I would fight you with my last breath to keep my past because I am proud of many parts of me, and I know they were born of my pain and mistakes, not my happiness. Even shorter version: Your past made you who you are today, you lose your past and you lose who you are, is it really worth it?