[magpi3]

This always made sense to me. Think of Super Mario Bros. No way you come up with something like that from a top-down design document. Probably slapped Mario on a screen, played with the physics a bunch, and threw a lot of different stuff at the wall to see what stuck before they came up with the final product.

[Larrikin]

Not sure about the original game but at least since the 3d age, Miyamoto is on record, saying that when making a new Mario game, one of the first steps is that is just fun to goof around with Mario alone in an empty flat void and mess with whatever new abilities they are thinking of giving him.