Some things in a building are decorative and some are holding the roof up. You find out which when you try to remove one.
Kindness becomes structural the way anything does — not by being declared, but by being used so often that the alternative stops occurring to you. Whoever always makes two cups when they make one isn't being generous each time; they've simply lost the version of the action that only makes one.
That's the quiet ambition. Not a virtue you have to keep summoning under pressure, but something worn deep enough into the routine that it survives a bad week.