Learn to laugh at things rather than negatively reminisce over them. Learn to be thankful for the things that you have and learn from the things you have done. Find ways to laugh at the mistakes you have made (hopefully not too serious of mistakes) and recognize how you have/can positively change your life from those mistakes.
Life is more than a 9-5 job. It’s more than pleasing those who tell you what to do. Don’t ponder over the jerks that fired you. Rather, use what you have done for them to benefit your future. If you are a writer, use your pieces to show other referable sources what you can do. If you are a coach, use your skills to coach another team and bring them up.
Recognize that life should be a healthy mix of work and play. Pleasure should come along with work and without work. So all in all, you should be experiencing pleasure more than anything in your life.