When the day is over we should self reflect to know what we did and how much it impacted on us positively or negatively but instead of self reflecting mostly we dwell on what we should've or could've done.
Sometimes things not go as we did them or planned them so we dwell that we should've done better in the end of the day. It's not the right thing! by doing this we only making ourselves anxious and restless.
We all face challenges and tough times because of our mistakes and our wrong decisions but it doesn't mean we should regret rather we should learn from our mistakes and try to take proper actions to make things workout but for now let it go.
Remember that tomorrow is an another day it means we've another chance to do things more properly.