If you treat the cashier worse than the CEO, your success already has a crack in it.

How you treat people with no power over you is the honest reading, because being pleasant to somebody useful is just self-interest with manners on. A gap between those two behaviours means the respect was never really respect. People notice the gap, including the useful ones, and it tends to decide what they say about you when it counts. Anything built on that foundation needs constant managing.

Watch yourself at a counter this week: your tone, whether you look up, whether you say thanks. If the version of you that shows up there is the worse one, that is the thing to work on.