I remind myself of this quote whenever I get pangs of self-doubt. The words you tell yourself are important in achieving your goals: if you believe you can, you will succeed. There will be plenty of people around to dish out some ‘realism’ to make you feel small but sensible career choices are illusory. Train yourself to be the voice telling you to keep going in the direction of your dreams. After all, you gain experience in trying to achieve your goals, and everything you wanted from accomplishing them! I think we owe it to ourselves to persevere.
Doing what you love is sometimes hard, always worth it.