Sometimes you just need to let people go. When it's time to fire someone, they usually know exactly why their being let go. Verbal and written warnings, being ignored are the hallmarks of difficult crew believing there's no reason to change.
Insubordinate crew fail to see their error, and the drama they create. When good crew believe troublemakers are getting away with things, moral slips, work performance drops and time lost calming upset crew increases.
Problem crew are shrewd manipulators, and that's why what's achieved holds higher value than what's said. There's no getting around the fact jobs are incomplete and below standard when crew focus their efforts elsewhere. Everything is measurable and have benchmark standards, that clarify when, how and who did their work and who did not.
The most common reasons for firing crew, are sustained underperformance and negative behavior.
When someone is fired, nobody wins. Because the employer and employee both need to rebuild.