JESUS' FRUSTRATION
Living our lives, trusting Jesus, does not mean that we will never feel futility or pointlessness. The clear implication of Isaiah 49: verse 4 is that Jesus felt this way. How many times did Jesus have to say, "ye of little faith."
"When the disciples failed to grasp the most simple spiritual truth for the fourteenth time, he must have felt that way."
"At the end of a hard day of verbal jousting with religious leaders who ought to have been the most responsive and were yet the most recalcitrant, he must have felt that way." ... "And when great crowds of people who used to follow him began to drift away, there is something almost plaintive in his question to the disciples, "You do not want to leave too, do you?"
(NIV Application Commentary-Isaiah, Oswalt)