What are the genuinely useful ideas in programming?

There is a really interesting article here about "What are the genuinely useful ideas in programming".

The comments are closed for that post, so here are the two things I would add to the list:

1. Index = Data(Algorithm + Data Structure): Google made this concept relevant, again.
2. Sensors, and networks of them (not to be confused with scanners (e.g. barcode, QR)): The Arduino and the Raspberry Pi made these important.