The major disadvantage that the colonists had going in to the Revolution was that they had no military to match that of Great Britain. Britain's was the strongest military in the world at that point. Britain had a professional army and a powerful navy. The colonists had militias and no navy whatsoever. They also had no support from any powerful countries in the rest of the world.
The major advantage that the Americans had was the fact that they would have to do less to actually win the Revolutionary War than the British would. The British would have had to conquer and pacify the whole of the 13 colonies. They would have to make sure that the colonists actually wanted to be done fighting and to reconcile with the British. By contrast, "all" the Americans had to do was to hold out long enough to frustrate the British into quitting. The Americans at least had a good chance at this because they were much more motivated than the British. The British soldiers were not fighting for any personal goals while the Americans were. The British public and indeed the government were not truly united behind the war. In this way, it was likely from a political standpoint that the British would tire of the war before the Americans would.
So, the major issue was this: would the British advantage in military force be able to overwhelm the colonies before the American political and motivational advantage took over and allowed the Americans to win when the British simply gave up on the war.