How do you know when it’s time to let someone go?

My deal breaker is when someone is dishonest.  I can work guide and train people that have a good work ethic, humble and willing to learn.

The buck stops when they are dishonest, throw their team under the bus, and don't take responsibility for their actions.  It's not the mistake that counts, it's how they handle the mistake that really lets me know what kind of person they are.