We recently had an employee leave our team, posting an extensive essay on LinkedIn, "exposing" the company and claiming a whole host of wrong-doing that went somewhat viral. The reality is, she just wasn't very good at her job and was fired after failing to improve following a performance plan by management. We all knew she was slacking and despite liking her on a personal level, knew that she wasn't right for what is a relatively high-functioning team. It was shocking to see some of the outright lies in that post, that effectively stemmed from bitterness at being let go.
The 'boy (or girl) who cried wolf' isn't just a story. It's a lesson for both the person, and the village who hears them.