Final answer:
In Shakespeare's 'Othello', Iago is bitter because Othello promotes Cassio to lieutenant instead of him, leading to Iago's revenge plot.
Step-by-step explanation:
Iago admits that he is bitter towards Othello because instead of promoting Iago to the position of lieutenant, Othello chooses to promote Cassio, who is a less experienced soldier. This situation is a critical catalyst for the tragic events that unfold in William Shakespeare's play Othello.
Iago feels his military experience and loyalty to Othello should have earned him the promotion. Iago's envy and perceived betrayal lead him to concoct a revenge plot that eventually triggers the downfall of many characters within the play, including Othello himself.
In the play 'Othello,' Iago admits that he is bitter towards Othello because instead of promoting him to the position of lieutenant, Othello chooses to promote Cassio.