Acknowledgment is a separate act from feeling. You can feel grateful for years without once saying it out loud to the person involved, and from where they stand, that looks identical to nothing.
The small ones especially go unspoken. Nobody thanks the colleague who quietly fixed the formatting. Nobody thanks the driver who waited.
Saying it costs about four seconds and changes the weather in a room. Whatever you noticed today and let pass, the noticing was step one, and step one is not the whole thing.