Why did the union general find that helped them to know lees plans for this battle?

The Union general discovered Lee's plans for the battle due to the accidental loss of a Confederate order, known as Special Order 191. This document, which detailed the movements and intentions of Lee's army, was found by Union soldiers wrapped around a cigar. The information allowed the Union forces to anticipate Lee's strategies, ultimately giving them a tactical advantage in the battle. This intelligence was crucial in shaping the Union's response and contributing to their success.