Peter catches a lot of crud. He proclaimed Christ and was called the Rock on which the Church would be built, but also denied knowing Christ and sank when trying to walk on the water.
But let us take a closer look at his little stroll on the Sea of Galilee. First, the context. John the Baptist had just been killed and Jesus withdrew. However, people followed to hear him speak. This is where we hear that famous story that we all remember from Sunday school: The Feeding of the Five Thousand. Afterwards, the crowds dispersed and Jesus sent the disciples away on boat while he prayed. The disciples hit some rough water and then see a strange figure on the water moving towards them...on foot. "And now," to quote Paul Harvey, "the rest of the story."
The disciples did what any red-blooded human would do - flip out. After Christ assured them, Peter calls out to him. This is often translated as "Lord, if it's you, tell me to come to you on the water," and this is often seen as Peter's first mistake (doubting Christ). But "if" could be better translated as "because". The NIV study note says it is "A condition assumed to be true." Peter is telling Christ that he will follow him, even in the seemingly impossible. And after having the faith to step from the ship to the sea, Peter gets scared and begins to sink. But here is where things get interesting: his first response isn't to try to save himself and swim back to the boat. Matthew tells us that he calls out to Christ for salvation.
I can only pray that when I start to sink, my first reaction is to call out to God.