Sometimes it just takes stepping out of the boat to realize you can walk on water. Peter wasn't God. He was just like the rest of us except that he wanted above all else to go meet Jesus. He didn't start to lose his stride until he stopped beholding Jesus' face and looked down at the waves.
So it is with all of us. Stay focused on the goal and keep your eyes on Him, not the circumstances. And when you find yourself slipping, call out. He will always respond and lift you back up.