John 1

John1:46"Nazareth! Can anything good come from there?" Nathanael asked.

Good question: "Can anything good come from there?" Here Nathanael's question is not a real question but rather a rhetorical question. We can see that in those times Nazareth didn't seem to have a good reputation. The people didn't expect anything good to come from there - above all not the Messiah!

In the same way Peter couldn't accept or believe in the words of Jesus completly. When Jesus told him to go fishing he answered:
Luke5:5"Master, we've worked hard all night and haven't caught anything. But because you say so, I will let down the nets."
When he said this he didn't believe that he would be able to catch any fish. He only obeys "because [he(Jesus)] say[s] so".
And when they caught a lot of fish, Peter "fell at Jesus' knees and said, "Go away from me, Lord; I am a sinful man!"" (Luke5:8) He confesses his unbelief and his ignorance of Jesus' position.

Nathanael - having a similar attitude (not believing that the Messiah could come from such a "bad" city) - also declared, after Jesus has told him he was and where he was before:
John1:49"Rabbi, you are the Son of God; you are the King of Israel."

Both of them, Peter and Nathanael, only believed because they have seen the power of Jesus. Their prejudices, knowledge and experiences have inhibited them from believing completly.
I hope that our knowledge and experiences will never hinder us from believing in God's power and grace. If yes, then hopefully there is a Philip saying: "Come and see"(John1:46)