"On each side of an alternating-tread ladder stair, every other tread is omitted,” Schuttner explained in Fine Homebuilding. As a result, “the distance between treads on a given side of an alternating-tread stair is actually twice the unit rise, which gives you more free tread area and therefore a safer stair in theory.

In theory, it’s safer because you can put more of your foot on the stair. In reality, people will get confused on which foot goes where and completely eat shit trying to use the stairs.