Practical Game Design : The Rule of Threes

The Three Amigos! starring Steve Martin, Chevy Chase, and Martin  Short

This is the first article in a series I'm calling Practical Game Design. (cross-posted here on Gamasutra)

The idea is to look back on the great masters of game design over the past few decades and extract some useful techniques from their games that we can immediately use in our own. I'll stick to specific examples as much as possible.

The first one comes from Shigeru Miyamoto himself, and although it might be known by other names, I'm going to call it "The Rule of Threes." This is a practical level design technique that introduces the player to new challenges gradually.
Here's how it works:

Before you challenge the player with a new feature, you first present it in 3 easy but varied situations.