I taught a computer concepts class to non-programmers and managers. One class problem:

--> DO i = 1 to 5

--> T0TAL = TOTAL + i

The value of TOTAL never changes.

When I pointed out the 2rd letter of the first TOTAL was a zero instead of an O, they understood bugs a lot better. Then, I told them the engineer that brought me the problem had been trying to solve it for a week.

It was a real popular class.