Read it through once

Wherever you find a man down there who believes in one of these theories you may turn to the next man and frame your talk upon the hypothesis that he does not believe in that theory; and after you have had experience, you do not take this course doubtfully, or hesitatingly, but with the confidence of a dying murderer--converted one, I mean. For you will have come to know, with a deep and restful certainty, that you are not going to meet two people sick of the same theory, one right after the other. No, there will always be one or two with the other diseases along between. And as you proceed, you will find out one or two other things. You will find out that there is no distemper of the lot but is contagious; and you cannot go where it is without catching it. You may vaccinate yourself with deterrent facts as much as you please--it will do no good; it will seem to 'take,' but it doesn't; the moment you rub against any one of those theorists, make up your mind that it is time to hang out your yellow flag.