The people of Nazareth thought they knew Jesus well. They knew his history, they knew his family, they knew what kind of child he was growing up. They had never seen him perform a miracle and they didn't truly believe that he was the Messiah. He told them the truth "hidden" in their hearts about their expectations for him, and they were so angry at him for it that they decided to kill him. (!!!) They used the excuse that Jesus claimed to be the Messiah when he was "obviously" not (they knew him too well), but they had never given him the opportunity to prove that he could do much more than they expected him to.
Are you capable of accomplishing much more than you realize? Have you put limitations on the people you know well, whose past failures have taught you what to not expect of them? Are you even limiting God Himself and the work He might want to bring about in your life? Moving beyond our preconceived notions allows us to surprise ourselves, to bless others, and to grow tremendously in our faith. If you think God "can't" bring about miracles in your life, He probably won't. Give Him the opportunity to prove that He can.