Critical Path

This is something gabbled at me by an old dragon of a Maths teacher many moons ago. She also predicted me a D at GSCE (Serves me right for disliking her son I guess) but I got 'A's at GCSE, AO and A level so shows how much you knew Mrs A!

Anyway the phrase isn't just used in the context of a personal vendetta against fearful students. Apparently it's part of an ancient Arabic proverb:

He who knows not and knows not he knows not: he is a fool-shun him.
...

Customer: Hello, what do you sell here?
Me: That depends who you are exactly
Customer: Me? Oh I'm just a middle aged woman with the usual mild anxieties.
Me: Oh well then I sell pills and natural herbal remedies that can redress the imbalances behind numerous health problems.
Customer: So medicine then.
Me: If you like, yeah in a manner of speaking. How about you call it the alternative to medicine.
Customer: Alternative Medicine! Brilliant! I've just realised ...