An experience, not a line.
Hakaras hatov has (unfortunately) become one of those Jewish buzzwords, like “Baruch Hashem” or “k’nieneh hora.” It’s something people throw in when they give a speech at an event or in other public forums. In that context, I usually find it meaningless.
Instead, hakaras hatov is a state of mind, a feeling, or an action prompted by sensitivity shown by someone else. It’s more than just “thank you” and covers much, much more than the act itself. It is a mindful recognition that whatever the other individual has done was not only “good” but that it connects to the greater good, changing the way you relate to yourself, them, and others.
So if you can say the words and move on, then it isn’t hakaras hatov. But if it changes you, and so you move on differently, then you’ve experienced the real thing.