Final answer:
The First Battle of Bull Run was shocking because it contradicted the North's belief in a quick war, exhibiting the Confederacy's formidable strength and leading to a reassessment of the Union's strategy.
Step-by-step explanation:
The outcome of the First Battle of Bull Run was a shock because it shattered the North's expectation of a quick and decisive end to the war. Instead, the battle revealed the strength of Confederate forces and the naivety of Union assumptions. The belief in a swift victory was so prevalent that spectators from Washington brought picnic lunches to witness the battle, expecting a Union triumph. Instead, the Confederate victory highlighted the determination of the South and dispelled the myth of an easy war. The loss led to a recognition of the war's scope and the need for a more serious approach from the Union, including considering emancipation as a war aim, as urged by abolitionists like Frederick Douglass.