In his article "The Structure of Gratitude," New York Times columnist David Brooks notes what he's learning about thankfulness:

I'm sometimes grumpier when I stay at a nice hotel. I have certain expectations about the service that's going to be provided. I get impatient if I have to crawl around looking for a power outlet, if the shower controls are unfathomable, if the place considers itself too fancy to put a coffee machine in each room. I'm sometimes happier at a budget motel, where my expectations are lower, and where a functioning iron is a bonus and the waffle maker in the breakfast area is a treat.

This little phenomenon shows how powerfully expectations structure our moods and emotions, none more so than the beautiful emotion of gratitude. Gratitude happens when some kindness exceeds expectations, when it is undeserved. Gratitude is a sort of laughter of the heart that comes about after some surprising kindness.