Henry changes in Gary D. Schmidt's Trouble by realizing his father's philosophy about trouble is all wrong. While growing up, Mr. Smith taught his family the principle, "If you build your house far enough away from Trouble, then Trouble will never find you" (p. 6). However, by the time Henry, Chay, and Sanborn are attacked by two fishermen at the base of Katahdin in Chapter 22, Henry has come to realize his father is all wrong; instead, "[y]ou have to live where Trouble is" (p. 264).
In saying the above, Henry means that you have to be willing to embrace trouble in order to do what's right. He also means that you can only make a difference in the world if you embrace trouble, not shy away from it.
Henry has two realizations the night the fishermen approach their camp that help him understand the need to embrace trouble. First, he comes to realize exactly how much Chay has suffered for having innocently fallen in love with an American girl, Henry's sister Louisa. If Chay had not wrongly been driven out of his home for having fallen in love with Louisa, Chay would not have run away, heading north; would not have encounteredthe two fishermen who were Vietnam War veterans in the chowder house in Portland, Maine; and would not have been wrongly attacked by the two fishermen, who mistook him for Vietnamese. In other words, Chay would not have encountered even more trouble as a consequence of having been made to suffer for falling in love. Henry's realization that so many wrongs have been heaped upon Chay help Henry reach his second realization, that Chay is innocent of Franklin's death since his death was only an accident. Because Henry sees Chay's innocence, he is able to see that Chay deserves to be defended against the unjust trouble the fishermen are bringing Chay in wanting to attack him. In being one of the first to take a stand and defend Chay against trouble, Henry is able to make a difference in Chay's life.