Being decent to people you’ll never see again is the purest version of decent there is.

How you treat someone you will never see again is the cleanest reading available, because none of the usual incentives apply. No reputation is being built, no favor is being stored up, nobody is going to mention it later. Whatever is left when all of that is stripped out is the actual thing. It costs almost nothing and it is still not automatic.

Give the next stranger a bit more than the situation requires, the door held, the name used, the actual thank you. You will not get anything for it. That is what makes it worth doing.