Staircase design is the intersection of structure, safety regulation, and human movement. The riser-to-tread relationship follows an ergonomic formula (2r + t ≈ 63cm) derived from average human gait.
Violate the formula — too steep, too shallow, irregular — and users stumble. Most staircase accidents happen on the last step, where the rhythm breaks. Consistent geometry trains the body; inconsistency catches it off guard.
Spiral and curved stairs are harder to descend than ascend because the body can't read the geometry in advance. This is why they are regulated differently for egress.
Related: acoustic-architecture, the-section-cut