Words have a longer shelf life than you think. People remember what you said way after you forgot saying it.

You speak from a mood that passes within the hour. The person listening files it somewhere permanent, especially if it landed on something they were already unsure about. That gap is why a throwaway line can sit in someone for years while you have no memory of the afternoon.

Since you cannot choose what sticks, say the good things more often than feels necessary. Give the compliment plainly, without softening it into a joke. And when something sharp comes out, go back and name it rather than hoping it evaporated.