Who begins too much accomplishes little.

- German

Explanation: I know this is an issue that concerns a lot of people (including me :) : we often start a lot of things, establish huge projects, but then we get bored and demotivated and abandon the project to start a new, even bigger one. 

What you need to do is think about achieving your goal, and ask yourself the question: "Am I sure I can get this done?"