Now let's look at the opposite:

"You don't know" is a sign of a bully. One may certainly ask for proof of some remark, or maybe change the statement to "we don't know". Pointing a finger is usually done by someone looking for a fight, to bring you down to the accuser's level of misery.

"You are wrong" is similarly an expression of hubris and anti-socialism. Providing proof to the contrary and letting the speaker divine his or her own conclusion is a way to allow the other to "save face" as the Chinese say.

"You don't understand" is the ultimate sign of a sociopath, especially when used after the first two expressions failed to produce the strife and misery intended. This is a sure sign to run - the person using this expression is simply a black hole of humanity trying to suck you into his or her bleak vortex.

Just my two sats...