"It is simply common sense at its best – rigidly accurate in observation and merciless to fallacy in logic."
Thomas Huxley, who had Darwin's back when he was propounding his theory on natural selection.
I like this as well...
"In the early stages of research, ideas are like hillocks on a landscape. So you design experiments to discriminate among them. Most hillocks shrink and disappear until, in the end, you are left with a single towering pinnacle of virtual certitude."