Abstract: To be grateful is a very common phenomenon in human society,and every person will have the idea or behavior to show his gratefulness.However,if we are asked why we should be grateful and why our society should be grateful,not all people know the answer.The reason should include three aspects: the essence of human's practice determines human being must depend on the nature,thank the nature and get on well with the nature;human's social attribute determines human being must depend on the society and get on we...