Life-Lesson #1:

Common sense is not so common.

Common sense is the knowledge or experience which most people allegedly have or should have.  But all too often in life you will see people do some really stupid stuff that you would think most reasonable people would not do.

For example, bathe with a toaster:

Bill Murray in Groundhog Day

Quote by Voltaire (aka François-Marie Arouet, 1694-1778), French writer, deist and philosopher.