There’s a concept in economics called sunk cost.
“In economics and business decision-making, a sunk cost is a cost that has already been incurred and cannot be recovered.”
This applies to life as well.
Have you ever seen someone being sad and depressed over something bad that happened in the past (usually long ago)? I’m sure you have.
I’m saying you shouldn’t be.
Regret is a wasted emotion.
The past is already gone. The cost has been incurred. It cannot be recovered.
(If it can be fixed, then don’t waste time being sad, go ahead and do it.)
Maybe you made a mistake. Maybe you made a bad decision, but that’s happened already.
You have no way to undo it.
The only thing you get by excessively focusing on your past is sadness, self-doubt, and depression.
Sure, you SHOULD fix what you can fix about what has happened, but what you cannot fix has to be accepted as it is. Doing this is a major key to happiness.
Let me end this with an example:
Say I give you a $100. On day one, you lose $50.
Day two, you’re sad that you were once a guy with $100 and now you only have $50. That’s the wrong way of thinking. What’s the point of crying now?
On day two, you’re actually just a guy with 50 bucks, not someone who lost 50 yesterday. This is because that’s the current situation you’re in NOW. That is all that matters.
You can only make decisions based on how your present resources can impact your future, not how your past resources can.
Your past, therefore, is irrelevant.