“In public and in private life, it often happens that there is simply no time to collect the relevant facts or to weigh their significance. We are forced to act on insufficient evidence and by a light considerably less steady than that of logic. With the best will in the world, we cannot always be completely truthful or consistently rational. All that is in our power is to be as truthful and rational as circumstances permit us to be, and to respond as well as we can to the limited truth and imperfect reasonings offered for our consideration by others.”