Milgram's shock generator rose in 15-volt steps. A design with one switch marked "450 volts, dangerous" would almost certainly have produced far less obedience. Why does the increment matter?

C. Because each step is barely different from the last

Gradual commitment removes the line: no step is a decision, and each one makes the next harder to object to without repudiating what you already did. It is foot-in-the-door driving something far darker, and it is why escalation in real institutions rarely presents anyone with a single obvious moment to refuse.