Some years back, I came across the phrase "Punctuality is the courtesy of princes." I do not know where it originated—perhaps some reader can tell me—but it struck me as embodying an important truth.
Suppose you are the big cheese—king, CEO, guest of honor. If someone else comes late to dinner, his dinner is cold. But the dinner can't start without you, so if you come late to dinner, everyone else's dinner is cold too.
It struck me in part in the context of the SCA, a historical recreation group of which I am a long time member; it actually has kings and princes and feasts, and if the King is half an hour late to the feast everyone else is likely to get food that has been cooling for half an hour.
Part of the justification for the phrase is the observation that lack of punctuality by the prince imposes a cost on everyone else. The other part is the observation that doing things for people only really counts if it costs you something. If the King knights someone, that's great for the recipient, but it does not actually cost the King anything. But being careful always to show up on time when your presence is necessary for other people does cost something, since quite often you have other things you would like to be doing, so it is a way of showing that the welfare of other people, in particular the people you are in some sense in authority over, matters to you.
The point is not limited to feudal societies or historical recreation. In the real world, I make my living as a professor. If one of my students is five minutes late, he misses five minutes of the class. If I am five minutes late, everyone misses five minutes of the class. If one of my students persuades me to revise his grade upwards or exempt him from some requirement of the class that he finds particularly difficult, that's great for him but doesn't really cost me anything, so is weak evidence that I actually care about his welfare. Taking the trouble to never come late to class, on the other hand, does cost me something.
Punctuality is the courtesy of princes. And professors.