Have you ever caught up in a situation like this? When you catch someone in the wrong, but they have a lot of influence? What are you gonna do?
It could be a violation of a sexual nature.
You could have seen someone steal something?
You could have overheard a diabolical plot against someone that trusts them.
Telling on someone can have dire consequences, especially if they can make you look jealous, or spiteful in the process.