Robert E. Lee was on a real hot streak before Gettysburg.
That ended with the Battle of Gettysburg. Lee and the Army of Northern Virginia lost an unbelievable amount of troops but they also lost the strategic advantage. They were unable to win a battle outside of the Southern States where they were provisioned and knew the land. They were mortal.
They tucked tail and headed back to Virginia to fight on for a little under two years.
Gettysburg marked the beginning of the end for Lee, who people now saw as being fallible.