Almost every day you will face situations that will challenge and stretch you. Your success in business, and life, is often determined by whether you overcome these challenges or not.
Whilst many things may stand in your way, the biggest obstacle is yourself. More specifically, the excuses, or the "but's" that you give instead of taking action.
Your achievements aren't driven by what you are capable of - the world is full of capable underachievers. You achieve what you believe you are capable of.