O world,To be direct and honest is not safe.I thank you for this profit, and from henceI’ll love no friend, sith love breeds such offence
Ironically mocking Othello's truthful words that suspicion is a sin, knowledge is a sin, by reminding him that all he praised Iago for was his honesty.
Though I perchance am vicious in my guess,As, I confess, it is my nature’s plagueTo spy into abuses, and oft my jealousyShapes faults that are not, that your wisdom,From one that so imperfectly conceits,Would take no notice, nor build yourself a trouble
IAGO QUITE LITERALLY IS HONEST WITH OTHELLO! He warns him that these suspicions, these inner thoughts are all a delusion, and yet Othello's insecurity and stubbornness refuses to believe it