We ought to write clearly and succinctly. A few minutes ago, I turned off my radio in disgust when I could handle no more of the deeply-flawed arguments being made by the broadcasters. Not for the most part. The fact that car accidents happen infrequently attests to the fact that most people act rationally most of the time. If average people did not behave rationally most of the time, we would not have cars, electricity, airplanes, and a thousand other things.
Rationality is common.
Rationality, however, is not universal. As Tim MacNeil points out, there are many times when normal people are irrational. They may also be ignorant, which is more common. The world is screwed-up. The rules most people attempt to operate under are doubly screwed-up.