The old believe everything, the middle-aged suspect everything, the young know everything.

Certainty changes shape as life goes on, and none of its shapes is the whole truth. Early on you have a clear system and few exceptions to it. Later you have collected so many exceptions that doubt becomes the reflex. Later still, having seen most things turn out stranger than expected, you find yourself willing to grant almost anything.

Notice which of the three you are running today, because it moves with mood as much as with years. If you are sure, look for the case that does not fit. If you doubt everything, let one claim through and test it properly.