What are some quotes or examples that show Harry's insecurity and how he overcomes it?

"More than anything else at Hogwarts, more even than playing Quidditch, Harry missed his best friends, Ron Weasley and Hermione Granger. They, however, didn’t seem to be missing him at all. Neither of them had written to him all summer, even though Ron had said he was going to ask Harry to come and stay." pg, 7

Harry well remembered putting it on, exactly one year ago, and waiting, petrified, for its decision as it muttered aloud in his ear. For a few horrible seconds he had feared that the hat was going to put him in Slytherin, the House that had turned out more Dark witches and wizards than any other — but he had ended up in Gryffindor, along with Ron, Hermione, and the rest of the Weasleys. pg. 77