Trenton was a large American force against a smaller German (Hessians) garrison. The Americans outnumbered the Hessians 2-1 there. Anybody could win under those conditions. It would take an idiot of monumental proportions to lose under those circumstances.

And I wouldn't exactly call Yorktown a victory accountable to George Washington. There were well over 5000 French Army troops led by the Comte de Rochambeau who played a key role, without whom Washington would have suffered another defeat. Without French help, and the fact that Britain was involved in wars in Thailand (Siam), Burma, India, China, Germany, Spain, and Russia during that same period of time, we'd be a British colony today.