There are too many things worth being grateful and appreciate from familiar sunshine everyday to a stranger's unexpected kindness. Everyone have received timely help from others in hard time. They are lifelong memories related to specific people in a particular time in your whole life, most of us could tell these vivid stories with when, where, who, why, what and how. However, in spite of these special "highlighted" things we found no difficulty expressing particular thanks, a majority of conditions, we have no awareness that we "should" be grateful to "someone" or "something".
David Foster Wallace's told a story that once upon a time,there are fishes with no idea what is water, pointing out that "the most obvious, ubiquitous,important realities are often the ones that are hardest to see and talk about". We are all fishes swimming hard to survive, we can clearly tell what we could see and what have happens to us or around us, ignoring the environment where we all live in, water.
The question is, as a fish,how can we react to "water", a invisible power. Keeping grateful in mind and taking the responsibilities to refresh water is a rational way.