Furthermore, Iago plans the death of Cassio, only because of Cassio " hath a daily beauty in his life That makes me ugly." ( v, i, 19-20). The qualities that make Cassio the Governor is the same qualities that make Cassio a better human being than Iago and Iago are aware with it. However, Iago's insecurity develops unlimited and undoubtedly hatred toward Cassio. Thus, Iago establishes strong envy towards Othello and Cassio considering the promotion of Cassio./.
The joyful lives of others enhance Iago's insecurity, the understanding of the difference between Iago himself and others effectively helps his envy to grow. First of all, after he sees the delicate sense of Othello and Desdemona, he thinks to himself, " Oh, you are well tuned now, But I'll set down the pegs that mask this music" ( II, I, 203-204). Iago's personality of envy slowly generates his insecurity, and he would act on it, which will eventually destroy the marriage between Desdemona and Othello. Secondly, Iago is jealous of the perfect life Cassio has; he plans to murder Cassio by enticing Rodrigo. ( I, iii, 383) Iago recognizes the goodness of Cassio would contract with his evilness, therefore, he would kill Cassio to satisfy his benefits.
Thirdly, after Iago notices all the good qualities Othello possesses, he declares, " The Moor, howbeit that I endure him not, Is of a constant, loving, noble nature" ( II, I, 284-285). Iago finds the good qualities other people has would annoying him and makes him dysphoric which would cause hatred and insecurity. Envy becomes the most significant part of Iago's personality and blends in his subconsciousness. Accordingly, Iago notices the contract between other's appearing beauty and his depravity gradually reinforce his hatred towards others and motivates him to act on the hatred.
Iago hears the rumor and suspects his wife Emilia sleeps with Othello, although he is not sure if it is true, he decides to act on his suspicion and possess powerful hatred against Othello.