An example of this that will be familiar to any programmer, and was taught to me in grade school, is "give orders to a malicious idiot." The teacher has the students write down the algorithm for a simple task, like "sharpen a pencil," with a wooden pencil and an old crank-operated sharpener as the props.

... Then the malicious idiot stabs you in the eye with the pencil. Oh, the malicious idiot was supposed to follow orders and only follow orders? Why didn't you say so?!