When you judge, you form an opinion about someone or something. Now add the "bad or wrong" prefix mis-, and you've got misjudge.
What is the root word of misjudge?
misjudge (v.)
"judge erroneously or wrongfully, form a wrong opinion," early 15c., misjugen, from mis- (1) "badly, wrongly" + judge (v.).
What is the base word in misjudge?
Origin of misjudge
First recorded in 1525–35; mis-1 + judge.