The devil makes you remember things in the past to make you sad. You need to understand this is his/her way of making you stop doing something that’s for your own good, and to think about the future. It is true you need to understand what went wrong in the past but you need stop thinking too long, and to merely see what you can fix if the same thing comes your way in your present life. You have to move on from there, and see what works for you in the future.