A side project is a place where nobody can tell you no. Everyone needs one.

Most work involves someone else with the power to approve it, and over years that shapes what you even think to propose. A project with no client and no brief restores a kind of authority you may not have noticed losing. It does not have to be good, or public, or eventually useful.

Start one that answers to nobody. Keep it deliberately outside your main work so it never turns into a second job, and let the only requirement be that you wanted to.