How not to be a mentor

[AllenThyl]

I would rather people not go through their lives assuming the worst out of others, regardless how "likely" it is that they are going to be irrational.

It's selection bias. The people that prompt others to actually speak up are the fringe, who are griefing others either by maliciousness ("I don't want to do AoE, I am practicing my single target rotation"), or by willful ignorance ("Don't tell me how to play" / "it's just a game" / "no one cares"). None of these attributes are conducive to a state of mind that will make them accept advice. Not knowing something doesn't mean someone is ignorant, but being ignorant will usually result in a lack of knowledge. That's where the 90% come from, and it's sadly a pretty good estimate. Even if the person in question doesn't speak up, some enabler typically will.