One of the most important ways to get better is seeking feedback from those around you.
If you have an employee that is underperforming, you must act to ensure that things turn around. You cannot afford poor performance on your team no matter how good things are going otherwise. See my best practices.
It is an axiom of leadership that you are what you tolerate. That bad behavior that you tolerate; that becomes the perception of you with your employees, colleagues and the marketplace.