Welcome to Fluther.
Hell of a Q to start with. Couldn’t you just ask something simple, like ‘Why are we here?’ No?
I think… we often try to imagine or pretend that we act for ‘what is best’, but then the question is “How did you calculate that?” And our minds are capable of such amazingly convoluted ‘logic’ sometimes, including misreading data, misunderstanding data that was read clearly, misinterpreting data that was properly read and ‘comprehended’ ... and rationalizing away the parts we read, understand and interpret correctly… so that no one can really answer that question.