When one jumps to a conclusion, what really happens?

Psychological term referring to a communication obstacle where one "judge[s] or decide[s] something without having all the facts; to reach unwarranted conclusions".[2][3] In other words, "when I fail to distinguish between what I observed first hand from what I have only inferred or assumed". [1] Because it involves making decisions without having enough information to be sure they are right, this can give rise to bad or rash decisions.