The first wants you to fail. It tells you there's not enough time in the day to make an impact, that you're not good enough, that you're meant to be mediocre.
The second acknowledges the steep climb, understands the risk, realizes the fear, but pushes forward regardless. The second voice is the occasional feeling you get that you CAN become great and DO anything you put your mind to.
Which voice are you choosing to listen to?
It's going to become more and more difficult. It never gets easier, you only get better at what you're doing. If you feel like giving up, like you've given your best effort but it's still not good enough, keep trying, you're probably closer to something remarkable than you think.
If achieving your dream was easy, you would have done it already.