Why did the capture of Fort Washington destroy the morale of George Washington's army?

It is believed that the Revolutionary War began with the Battles of Lexington and Concord. However, it actually began with a siege. This siege was called the Siege at Boston. The British army wanted to move across Boston and the militia stood in their way.

Then the siege lasted for almost a year before the British Army left Boston. In 1776, near the start of the war and after the siege which was deemed a success and victory for the patriots.

Instead, the Battle of Fort Washington began with an attack by the British. Washington believed that he could secure the fort, but he couldn’t. They surrendered and this was the first defeat that the Patriots felt. In turn, this destroyed the morale of the army.