Many therapists reach false conclusions due to biases. The three main biases are: 1) confirmation bias 2) anchoring 3) overconfidence bias.

Confirmation bias is when a therapist begins with a conclusion (diagnosis) and puts added weight on certain statistics to prove the conclusion.

Anchoring is when a therapist gives too much weight to his or her first impression.

Overconfidence bias is when a therapist puts too much faith into his or her knowledge or opinions.