Learn the things you find you, do not, but will need to, know.
Learn what does thing efficiently that you are now doing.
Learn things that will expand your reach by adding new tools to your toolbox.
Do more things.
Adding targeted knowledge:
Increases your value
Raises your Self Esteem
Increasing one's technical competence:
Adds to one's toolkit
Expands the expertise we can bring to bear on the client's system. Sometimes the littlest extra insight solves a raft of technical problems.
Professionalism requires that we do this anyway; there is no such thing as standing still
One could also use this as the opposite of IfItCantBePerfectDontBother. If you don't know the perfect solution, at least pursue the best partial solution. If you don't understand the whole problem, work on the part you do understand.