Why would you ever waste time doing anything that doesn’t move you forward? Yet that is what many of us to on a daily basis.
From worrying about petty problems, to imagining what it would be like if your situation was different, to wallowing in self-pity, many of us spend a portion of our days doing something that is counter-productive to our personal development. Over time, all of this negativity adds up.
We should focus on things that move us forward. Instead of worrying about how a job interview went, start planning how you will improve your chances of getting that job. Instead of worrying about how an exam went, start reviewing the content and improving your understanding of the exam material so that you can do better in your next courses (which will no doubt build on material that was covered previously).
Eventually, you will build up the habit of constantly improving yourself and moving forward, instead of staying still in negativity.