Answer :
He attacked the Hessians in the winter because he knew that it was against the usual battle tactics of the era to attack in winter. He did this so he could give a moral boost to his men and keep them enlisted.
George Washington, General of the Continental Army, attacked Trenton to give some confidence into his troops, because they were losing all of the battles fought. It was a surprise attack, and the Hessians were celebrating, and were caught unexpected by the attack, so the result was decisive victory for American Continental Army. Hope this helps!
