Mt. 17:14-20 relates the story of the father of the epileptic boy who begs Jesus to heal his son after his disciples are not able. As this story relates, Jesus was not too impressed with the "little faith" of either the father or of his disciples which resulted in the failure to heal the boy.
We must not underestimate Jesus' expectations for us, especially in regards to our maintaining a firm faith in him. When the father of the epileptic boy reports to Jesus about his his disciples' failed attempt to heal his son, it's almost as if "this generation"'s lack of faith and Jesus' intolerance with it came to a head. His expression of remorse, "O faithless and perverse generation, how long am I to be with you? How long am I to bear with you?", was prompted by the father's request for something which may not have been necessary were his disciples to have had adequate faith. Jesus would not have reacted so were a certain level of expectation he had for his disciples not let down. We, too, must respect our Lord's expectations for us and not fall into the trap of asking things of him without simultaneously maintaining a firm faith.