Perception.

All we can go on really is how we perceive others actions (or what they say) and the intent that we can gather from what they do (or say).

And all of this runs through our filters of past experience and what we've perceived others intents to be in relation to the things they've done (or said).

For example: I'm really quick to pick up on people using emotionally abusive/manipulative language or acting in abusive/manipulative ways, this is because I've (unfortunately) had so much experience with abusive/manipulative people. I've spotted it incredibly early in relationships, not only my own but the relationships of others. People don't like getting called out on it, and people really don't like it getting called out when they don't see it in their friends or partners.

"They're not like that with me."

"They're only like this sometimes."

"Well I did kinda deserve it."

I call it out when I see it, because abusive and manipulative behavior left unchecked will only fester.