Dad and Robert Heinlein are right

The internet credits Robert Heinlein with saying "Man is not a rational animal, he is a rationalizing animal," but my dad told me that when I was very young. Since all writers burrow things away in their subconscious, my guess is Heinlein picked it up somewhere, maybe from Twain, or maybe it's just one of those observations that smart people eventually make.

When I was older, Dad phrased it more bluntly: "Your problem is you think people are rational." I can't remember how I answered, but what...