The answer is "jumping to conclusions".
Jumping to conclusions is a mental term alluding to a correspondence snag where one "judge[s] or decide[s] something without having every one of the actualities; to achieve unjustifiable conclusions". As it were, "the point at which I neglect to recognize what I watched direct from what I have just gathered or assumed". Because it includes settling on choices without having enough data to make sure they are correct, this can offer ascent to terrible or impulsive choices.
