The Top 10: Things You Understand When They Are Explained But Forget Immediately

‘I read clever articles and nod along knowingly and 10 seconds later it’s all gone’

What is a hedge fund? Erm... (Getty/iStock)

1. Hedge funds. So-called because they originally hedged their risk by betting against the market. Not the same as private equity funds.

2. Bayesian probability. Fancy kind of trial and error.

3. The three-door problem. On a game show, a car is behind one of three doors. You choose a door, and the host opens another door, which is empty. Should you now switch to the remaining door? Yes, but why?

4. First and second cousins, once or twice removed. “Drains out of me like a colander,” said David Robinson. Also nominated by Colin Rosenthal.

5. The offside rule. Nominated by Steve Clarke and supported by Jordan Tyldesley (“Not me, but for many, in my experience”).

6. Both Modern Monetary Theory and the refutation of MMT. Nominated by Julie Plummer. Colin Rosenthal suggested most economics: “I read clever articles recommended by people like Oliver Kamm explaining why national economics is absolutely nothing like household economics and nod along knowingly and 10 seconds later it’s all gone.”

7. How to use layer masks in Photoshop. Nominated by Timothy Auger. I’m sure I would briefly understand it if it were explained to me. Other suggestions included “pointers in C++”, from Hugh Jympton.

8. The square root of -1 and why it matters even though it doesn’t exist. James Hawes said: “My father could get quite excited about that one after a Talisker or two.”

9. “What’s happening” and “Who people are” in whatever my wife is watching, said Niall.

10. Why the sky is blue. Nominated by Chris Hogg. I think the answer is unmemorable because it is essentially, “because it is”, or rather: the shortest wavelength of most visible light looks blue because it does.

Next week: People who understood Twitter centuries before it was invented, such as David Hume, who said: “Disputes with men, pertinaciously obstinate in their principles, are, of all others, the most irksome.”

Coming soon: Political rows that seemed huge at the time but now seem oddly quaint, such as the pasty tax (thanks to Matt Chorley).

Your suggestions please, and ideas for future Top 10s, to me on Twitter, or by email to top10@independent.co.uk