* He was outnumbered by William's forces. William had brought a large army to England, which included a significant number of cavalry. Harold's army was smaller, and it was not as well-equipped as William's.
* He was betrayed by some of his own men. Some of Harold's supporters defected to William before the battle, and they provided him with valuable information about Harold's plans. This gave William a significant advantage in the battle.
* He was killed early in the battle. Harold was killed early in the battle by an arrow to the eye, and his death caused his army to lose heart. This allowed William to win the battle and conquer England.