In most of mankind gratitude is merely a secret hope of further favors.

Thanks can quietly function as an investment, keeping a useful person warm rather than acknowledging what they did. The suspicion is unkind and worth entertaining anyway, because the difference shows up in whether you stay grateful once someone can do nothing more for you. That is the test, and it is easy to run.

Think of somebody who helped you years ago and has since dropped out of usefulness entirely. Tell them, with nothing attached and nothing wanted. Gratitude that costs you a little and returns nothing is the version that was real.