Wasting someone’s hour is taking something they can never get a refund for.

Time taken from someone cannot be returned in any form. An hour spent waiting for you, or sitting in a meeting that did not need them, is gone from a supply nobody knows the size of. It is easy to treat lightly because there is no bill and most people are too polite to mention it.

Before you take someone’s time, decide what it is for and how long it needs. Start when you said, end early when you can, and treat being ready as part of the appointment.