Everything that a person does when they are taken by surprise is the best proof of what he really is. That which breaks away from the tongue, before it is time to suppress its impulse, betrays the true essence. If there are rats in the basement, then you are most likely to see them if you enter unexpectedly. But no surprise breeds rats; it only prevents them from hiding in time. Nor does the surprise of the excuse or the excuse make me quick-tempered; she only discovers my hot temper.
– Clive Staples Lewis, “Just Christianity”