Final answer:
Brutus' stab was seen as the worst wound Caesar received because it represented a profound personal betrayal from someone Caesar trusted deeply.
Step-by-step explanation:
The wound that Brutus gave to Caesar was considered the worst because it symbolized the ultimate betrayal. Caesar's shock at Brutus' participation in the assassination, encapsulated by his famous last words, "Et tu, Brute?" ("You too, Brutus?") as reported by Shakespeare, underscored the depth of Brutus' betrayal. Brutus was not just another senator; he was perceived as a son to Caesar, and his participation in the murder dramatized the collapse of personal and political loyalty, which was seen as a grievous wound to the spirit and authority of Caesar.