Why did Max wait so long to reveal his illness to the family in The Book Thief?
The answer to this question involves inference on the part of the reader in that Max never really tells us why he waits so long to tell the family that he is sick. The answer has more to do with Max’s character: he is a fist-fighter and likes to believe that he can handle whatever comes along on his own. In reality, Max cannot handle everything by himself, mostly because he is Jewish in the middle of Germany during World War II.
We learn this part about Max’s personality after Max eats the pea soup at the Hubermanns'. After Max eats, he immediately throws up because his stomach is not used to having so much food. At this point, Max fumbles for words:
Thank you. For Max Vandenburg, those were the two most pitiful worlds he could possibly say. Rivaled only by I’m sorry.
Even though Max is not sick at this point, we learn how independent Max wants to be. Unfortunately, at this time in history, a Jewish person like Max is unable to be independent, especially when he is sick. We can infer, though, that Max wants to try to remain independent even through sickness. As a result of this independence, Max waits too long to tell the family he is sick.