History provides context. Without knowing the past, we can never appreciate the present or plan for the future. By history, I don’t just mean national or world history but even history of a person. Without understanding where a person is coming from, what his/her experiences, learnings, unlearnings have been, we can’t possibly judge a person in entirety.
Say, I have a stomach ache. My doctor will not just ask me my symptoms but also what & from where I had eaten my last meal & also my past medical record. Only then will he/she be able to diagnose whether I have taken ill due to consuming leftover/street food or because of some other reason. Similarly, when trying to make sense of a human, we MUST, as a habit, try & look back into the life of that person.
Just seeing his/her present behavior could lead us into taking an erroneous decision. No need to be in a hurry, analyse situations & then form opinions.