Much of Bud, Not Buddy includes the resilience of ten-year-old Bud. Near the beginning of the book, when Bud goes to live with the Amoses, they treat him badly; Todd, the Amos son, beats him, and Bud says,
There comes a time when you’re losing a fight that it just doesn’t make sense to keep on fighting. It’s not that you’re being a quitter, it’s just that you’ve got the sense to know when enough is enough.
And yet, he doesn’t quit. Just a moment later, he says,
He could kiss my wrist if he thought I was going to let him whip me up without a good fight.
Mr. and Mrs. Amos lock him in their shed. Bud battles what he believes to be a vampire bat (“I wasn’t about to let this vampire suck my blood dry without a war, he could kiss my wrist if he thought that was going to happen”) and some hornets, and he then breaks a window to escape. He gets revenge on the family by making it appear as though Todd wet his bed (which Mrs. Amos hates) and goes off on his own again.
When Bud wants to get in line at the mission, a man standing with a black strap tells him he’s too late. Bud keeps trying to explain why he should be allowed to line up, until the man pulls out the strap.
Later, when Bud misses the train west, he doesn’t get discouraged. He remembers what his mother said about one door closing and another opening and says, “Maybe I should stay here in Flint.” Instead, he goes to the library, makes a plan, and heads to Grand Rapids to find the man he believes is his father.
When Mr. Lewis pulls over to pick up Bud, and Bud believes he is a vampire because of the human blood in the car, Bud doesn’t freeze. He locks both doors before Mr. Lewis can get in and tries to drives away.
Bud sticks around Herman E. Calloway when he believes he is his father, but Mr. Calloway says he isn’t. Eventually, Bud learns he is his grandfather, and he is able to live with him.
One theme running through the novel is that of never giving up. This theme became Bud's mantra partly because of a saying his mother told him. The author writes that Bud's mother always said that when one door closes, another door opens. This saying reflects the attitude of his mother and it was instilled in Bud.
Throughout the story, Bud never gives up the quest to locate the man he believes is his father. With each obstacle placed in his way, Bud lives the quote he heard repeated by his mother, and moved on looking for the next open door.
When Bud was placed in a new foster home where he was mistreated, he managed to get away and find a familiar resource, the library. Once he realized the librarian had moved, he followed a friend to a new location, a shanty town where he attempted to get on a train out of town to find his father. This did not work out, so Bud set out walking. However, a man picked him up, fed him and eventually got Bud to the place where the man he believed was his father, Calloway, was playing with his band. Bud never gave up believing that Calloway would accept him as his own. Through Bud's persistence in getting to know Calloway, he finds that he is his grandson, not his son. Bud finds a new home with his grandfather.