Harford Worstall. #1 is "Incentives matter" and that's important and useful enough that it doesn't much matter what #2 is.
UPDATE: the author of the piece is Tim Worstall. I apologize to Mr. Worstall and thank him for the correction.
For much more on the "Two things" game see this collection. Examples:
The Two Things about Accounting:
1. The trial balance must balance.
2. There's a lot of "grey area."
The Two Things about Computer Programming:
1. Idiocy increases faster than idiot-proofing.
2. All compiling errors boil down to a missing semicolon.
The Two Things about Star Trek:
1. Don't beam down in a red shirt.
2. You can always talk evil computers into destroying themselves.
The Two Things about Writing:
1. Include what's necessary.
2. Leave everything else out.