The Appreciation of a Nation
It happened on the seventh day that some of the people went out to gather, and they did not find. (Ex. 16:27)
After Moses said that no manna would fall on Shabbos, Dasan and Aviram tried to trick the people into thinking that the manna had fallen on Shabbos by scattering some on the ground at sunrise. Birds came and ate all the manna they had spread before the Bnei Yisroel woke up. Had the people seen even a small amount of manna on Shabbos after Moses had said that it wouldn't fall might have caused a tremendous amount of confusion, which could have led to a rebellion against Moses. Once a year we show appreciation to the birds by feeding them bread.(1)
Birds naturally eat. By eating all the manna they didn't do anything that goes against their nature. In fact they didn't even know that they were doing a great kindness, they just saw bread and ate it. Why then do we reward them yearly?
It is true that birds eat, and eating the manna was not an act against their nature. However, because the eating of the manna was favorable for us, we need to be grateful for it. Being grateful is not dependent on what drove the benefactor to do the act; rather it is for the one receiving the kindness to show appreciation - regardless of the intentions of the giver.
Focusing on what you're lacking leads to misery. When one has a sore throat he can focus on his throat - which will then make him gloomy, or he can focus on the fact that he's breathing fine, his business is going smooth... On average, 90% of things in our life are good. The key to happiness is to be appreciative - focus on the 90%!
1. There is a custom to put out bread for the birds on the week of Parshas B'shalach, in gratitude for the fact that they ate the manna.