The answer is: Achan

Josh 7:1 - Achan's sin was the cause of the defeat at Ai resulting in 36 Israelites being killed in the battle.

When we dive into the story of Achan in the Book of Joshua, it's fascinating how one individual’s choice led to consequences for many. Achan’s decision to plunder treasures from Jericho, which God specifically commanded should be devoted to Him, teaches us about the ripple effect of sin. When Achan took a beautiful cloak, silver, and gold, it wasn’t just his disobedience; it resulted in Israel's defeat at Ai and the tragic loss of 36 lives.

This story also beautifully highlights the concept of collective responsibility, a theme echoed throughout the Scriptures. In ancient Israel, the fate of the community was often tied to the righteousness or sinfulness of its members. In other words, one person's action could disturb the peace and favor enjoyed by the entire nation, linking personal choices to a greater societal outcome. This reminds unity can be both empowering and precarious.

Interestingly, the city's fall of Jericho itself involved some unexpected strategy—marching around the city walls for seven days until they fell down! Such demanding yet unusual military tactics served to show how faith and obedience outweighed mere human fortifications.

With Achan’s sin, it's also noteworthy to examine how temptation often causes us to dismiss the greater good for fleeting desires. It evokes questions about our integrity and our adherence to principles set before us. Achan's story is a profound reminder: each desertion from integrity doesn't just impact us alone; it has the potential to affect everybody in our community.