Everyone has them. "I didn't know what to say!" Times when you are silenced - overwhelmed with embarrassment, gobsmacked, dumbstruck - because someone confronts you with a situation, and you have no idea how to respond.
Little wonder people would rather say anything than ask someone with a terminal disease about it. They prefer to avoid talk about politics, and "don't do God". Or - in a new chapter in the history of impossible social predicaments - they click "Confirm" rather than "Ignore" when someone they barely know asks them to be a friend on Facebook. After all, being handed a spade to keep digging is possibly even worse than being given a rope to hang yourself. If you hang, you die; if you dig, you live to recall the hideous moment - and die a little death each time you do.
So it may come as something of a surprise to learn that philosophers have argued that such moments are some of the most valuable in life.
"To err is human," the Latin adage goes - implying that mistakes are humanising. Why? Partly because everybody makes them and so everybody should be charitable about them: it will be you some time soon. And, more interestingly, because embarrassing impasses are actually moments of opportunity when you can learn something new. The shock of such moments can pierce otherwise impenetrable egos. As Sigmund Freud realised, in pondering the power of free association, it is what you mean not to say that is in fact most revealing of yourself.
Alternatively, such precipitous moments are at the heart of Socratic philosophy: Socrates's method was to talk his interlocutors into silence, because that way they reached the limits of what they knew, and were in a position to learn more.
"Even the sage trips over the truth seven times a week," goes another saying, which is to say that it happens every day. There is advantage to be gained in the sage so doing. For a really good error is one that can lead to an excellent correction.
Moving beyond the personal towards the great collective pursuit of knowledge, such a process, according to Karl Popper, is at the heart of the scientific method: the best hypothesis is the one that is the most easily falsifiable. To put it another way, the very guardians of truth in our society, scientists, are nothing if not in the business of making mistakes. Think of Ptolemy, Newton or Lamarck. They were wrong, but they were prepared to stick their necks out and, as a result, we are all the better for it. Perhaps one day people will say the same of Einstein, Bohr, or even Darwin.
The lesson would seem to be this: don't mind the risk of saying the wrong thing. Rather, say the wrong thing, but brilliantly.
Mark Vernon's "What Not To Say: Finding the Right Words at Difficult Moments" is published by Weidenfeld & Nicolson (£12.99, hardback) on 1 November