What changed Oskars grandfathers decision to stop writing to his son after 9/11

"He spends years writing to his unborn child, a child who can be either Thomas Jr. (Oskar's Dad) or the baby that Anna was pregnant with when she died in the bombing. But Grandpa only sends one letter, a letter that Thomas marks up in red pen. Grandpa only meets his son once, when he came to Europe posing as a journalist. Neither admitted to the other who he was. He returns to New York shortly before Thomas Jr. dies in 9/11."

Explanation:

c, his tragic flaw to cause his downfall

the significance of the title, "the passing", is related to the fact that the main characters, who are three african-american descendant women, are passing as white. this means that, because of their light-coloured skins they look like white women. one of the three friends, clare, is married to a white man and she lives in a white community and she has never told her husband that she is black. the title can easily be connected to the idea of pretending to be someone you are not and of losing your real identity in order to be accepted by society.