The rabbi and scholar Jonathan Sacks wrote, "How tragic it is that we so often keep our gratitude to ourselves, speaking it aloud only when the person to whom we feel indebted is no longer here, and we are comforting his or her mourners." It is a tragedy, indeed.
■ Naturally, some time often needs to pass between a good act and a display of gratitude -- you don't stop a person in the process of dropping off a casserole and have them wait in the doorway while you hand-write a thank-you note. And in some cases, a good deed long remembered can bring great joy when acknowledged long afterward -- consider the kindergarten teacher greeted with love by a graduating high-school senior.
■ But it generally betters us to do the work of recognizing others for their good works earlier rather than later. Yes, good behavior should generally be its own reward. But humans are social creatures, and we are formed by the norms and institutions around us. If we want to see more good choices being made in this life, then we need to praise (and be seen praising) those good works as early as can be sensibly justified. Reinforce good behavior and you might just get more of it.