on the stoicism side, it involves accepting responsibility for the effects of your actions on the world. There is much you don't control, but your choices given that have created your world. I think there is a natural willfulness that strongly wants to deny this, but self reflection should always be guided by what is useful/helpful. So understanding how you have shaped the world helps you decide what to do now with what you immediately control.

it's unhelpful if you just tell yourself you should have done x, but helpful if you understand why and when you should do x in the future

You are a product of the thoughts you choose to focus on, it physically changes your brain. There's no reason to engage in unhelpful thoughts, and not doing so reduces the strength of those negative pathways