What life lesson did you learn in school?

The number one thing I should have learned in school was interpersonal interaction. Unfortunately they never did give a grade on that and as a consequence I am a total failure at it now (OK, maybe not a TOTAL failure, but still I shouldn't feel this uncomfortable with social interactions.) I always wondered how school kids handle history now -- there are three more decades of it to learn since I have been in school. And the USSR is now a dozen different countries ... The one subject that applies to my life right now from school is algebra, but only because my job is to create Excel and Access solutions to various business problems. To simplify the approach algebra is invaluable .