Ah, the power of possibility!
To "think I can" is to view one's place in life as a forward moving, progressively thinking phenomenon.
The moment we allow our minds to focus on the doubt, the fear, the uncertainty... this is the moment the fat lady sings -- because at that instant it's game over.
A road trip is a good analogy, it seems to me. To get anywhere, one must get out the map and find the YOU ARE HERE spot. Then there's the step of determining where you want to go... because if you have nowhere you want to go, that's exactly where you are going to end up: NOWHERE!