I don't have a direct answer for that, of course, but I have what I would call a suspicion. I believe that Jesus was born as a normal human being. During his life, he became so close to God that Jesus the human essentially ceased to be and he was the living will of God. If the account of Jesus' baptism is a historical account, and not an attempt to link him to John the Baptist, then I wonder if it was the moment of epiphany for him, that he gave himself up completely at that point. If so, then my answer to Shane's question would be that he might have deviated from the will of God before that point.
There are times, too, in the gospels when I feel like it is the human Jesus speaking. In the garden of Gesthemane, for example, when he asks "Take this cup from me. Yet not what I will, but what you will." And of course on the cross, "My God, My God, why have you forsaken me".
Although a lot of people consider my view of Jesus to be blasphemous, I find that it gives me great hope. The things Jesus did and the way he acted are not impossible for us. The closer we align ourselves to God, the more we become like Jesus. I have often heard people dismiss some of Jesus' teachings as impossible for us to follow because we are only human. I do not believe that, and I know that the early Quakers did not believe that as well. George Fox spoke of us being restored to the state of Adam before he fell:
And the Lord showed me that such as were faithful to Him, in the power and light of Christ, should come up into that state in which Adam was before he fell
And that brings me back to the verse in Mark, and closer to William Barclay's view of Mark 10:18, which is that we shouldn't concentrate on "being good", we should concentrate on being in God. Out of that comes the good.