I am generous with my money.

The most generous people are the hardest to catch at it.

They have already paid before the bill reaches the table. They mention nothing. Six months later you find out by accident that they covered something and never intended you to know, because the whole design of the thing was that you should not feel owed. That is the difficult part — not the giving, which is straightforward enough, but doing it in a way that leaves the other person lighter rather than indebted.