In Mark 9 there is a story of a man who brought his son to Jesus' disciples. His son had seizures and had been sick since he was a child. The disciples couldn't heal him. Jesus came onto the scene and the father said, "If you can do anything, take pity on us and help us."
Jesus answered, "If you can? All things are possible to him who believes."
Immediately, the boy's father said, " I do believe; help my unbelief."
I love the father in this story. He realized his mistake in saying, "If you can..." He realized his faith was small and he needed help. Like Jacob, he wouldn't let Jesus go until he blessed his son. After asking Jesus to help him have more belief, Jesus immediately healed his son.
This man's prayer to Jesus has helped me in my life. Sometimes I just say to God, "Help my unbelief," and He does.