"The Moor, howbeit that I endure him not, is of a constant, loving, noble nature, and I dare think he’ll prove to Desdemona a most dear husband. Now, I do love her too, not out of absolute lust—though peradventure I stand accountant for as great a sin—but partly led to diet my revenge, for that I do suspect the lusty Moor hath leaped into my seat (II.i.267-275)." -Iago
Plays are a little unique in that there can't really be a 1st person point of view obviously; a play is either 3rd person limited or omniscient. While most plays let the audience in on the plot, not many do it from the point of the antagonist. Through this device used by Shakespeare, the audience knows everything the villain is about to do. Although Iago is definitely not a character to sympathize with, the audience finds itself wondering and to see if this plan will actually work and unfold as told. Also, while Iago is far from sane, he exhibits common human fears and emotions. Unfortunately, it isn't uncommon for a man to suspect infidelity, like Iago. While his fear may be unwarranted, it's plausible. The imperfect, evil, maniacal, and deceitful Iago definitely has trust and self-confidence issues and feels wronged by the world and must concoct an evil plan to get even with everyone.