The piece of evidence that best supports the theme that there is honor in defeat is:
“I shall have glory by this losing day, / More than Octavius and Mark Antony.”
This line expresses Brutus's belief that even in defeat, there is a sense of honor and nobility in his actions and choices. He suggests that the honor he gains from standing up for his principles and the values he represents outweighs the outcome of the battle, emphasizing that true glory can be found even in loss.