Are you referring to the poem "Tears, Idle Tears" by Alfred Lord Tennyson or the short story "Tears, Idle Tears" by Elizabeth Bowen?
I assume it's the poem, so here goes:
As the speaker is looking into the fields one Autumn day, s/he is reflecting upon the deaths of friends and loved ones. He describes feeling tears associated with these deaths as being "Tears from the depth of some divine despair." There is no particular death that causes the speaker to from tears, since, after all "...tears, I know not what they mean." What causes the tears is most likely the finality of death and the thought that "of the days that are no more."
The plot of the story is closely related. Enotes offers a strong recap here:
Seven-year-old Frederick bursts into tears in the middle of Regent's Park on a beautiful, sunny May afternoon as he and his mother are on their way to the zoo...Frederick cries often and long. He never knows why or what happens to make him cry. He just cries. Nothing matters to him when the tears take over; this day in the park his mother refuses to take him to the zoo, but he does not care. His lack of self-respect makes others look at him and respond in unkind ways; he gets no sympathy. His mother tells him at least once a week that she does not know how he will fit in at school because of his crying. Mrs. Dickinson hates the fact that when she takes a privilege away from him for crying, he seems not to care. She seldom openly punishes him, but she rebukes and belittles him almost constantly. When he seems to feel no emotion about not going to the zoo, she tells him she wonders what his father would think of him. She goes on to say that his father, a pilot who had died after an airplane crash, used to be so proud of him that she is almost glad that he is no longer with them. After this strong reprimand, Mrs. Dickinson walks on ahead so as not to be embarrassed. She tells Frederick to pull himself together before he catches up to her.