Final answer:
Iago exploits Cassio's weakness of alcoholism, leading to Cassio's downfall and advancing the tragic plot of Shakespeare's Othello.
Step-by-step explanation:
In William Shakespeare's play Othello, Iago exploits the weakness of Cassio's alcoholism. Cassio is portrayed as a man who cannot hold his liquor, which Iago manipulates to disgrace him. During a celebration, Iago encourages Cassio to drink, despite Cassio's initial reluctance and his admission that he has a poor tolerance for alcohol. Once Cassio is inebriated, Iago provokes a fight that results in Cassio acting in a disorderly manner, eventually leading to his demotion by Othello. This incident seriously damages Cassio's reputation and plays into the overall tragic progression of the play's events. Iago's cunning exploitation of Cassio's vulnerability drives the plot forward, weaving deceit and mistrust among the characters.