You've heard the story. A roadsweeper retires, and in his retirement speech he tells the story of how, thoughout his career he has always used the same broom. A listener is sceptical about this and comes up to him after the dinner to ask him about it
"Its true" the roadsweeper says "the same broom. Though I had to change the head ten times and the handle twelve"
Now think back 10 years. Are you the same person. Would you act exactly the way you acted back then with the knowledge you have now? Do you really have the same values, the same responsibilities, the same skills and the same desires. My bet is you don't. While you might have a continuous memory of experience - just like the roadsweepers broom had a continuous pattern of use, you're only as much the same person as the broom is the same broom.
("But I have many things the same. I have the same parents or the same spouse." Yes you do, but my sister has the same parents as me, and she isn't the same person)
I said that you had a continuous memory of existing. But you don't. The likelyhood is that sometime in the last 24 hours, you have a mysterious gap in your memory... it probably happened sometime between when you lay your head down on the pillow last night and when the alarm clock rang this morning.
So are you the same person you were yesterday?
Not quite. Yesterday, before I fell asleep, I was tired. Today I'm awake and energetic. Different day, different person. Similar person, but not the same.
So why spend quite so much time worrying about what someone else did yesterday? Or last week. Or twenty years ago?
If you were a time traveller who had just jumpped into your body (and at this point I have to acknowledge that I get all my self help tips from Quantum Leap... except for when I'm getting them from Blake's 7) you wouldn't obsess about what you might have done differently. You would just get on with making the best of what you've got from where you are now.
Come to think of it, are you the same person you were when you started reading this?