You're reading way too much into fizzbuzz. Whenever I get a problem like this on a white board I know that it's just a screening question, so I solve it. Solving this toy problem is nothing like solving actual problems in the real world. If you use fizzbuzz for its intended purpose, great. If you're doing it like this, you're going to reward the people who are incompetent enough to need to draw out every implication of a 3 line function.