A foregone conclusion Why Should I Care
Why Should I Care?
Iago might just be literature's most impressive master of deception. Iago plots with consummate sophistication, carefully manipulating Othello (without any real proof) into believing that Desdemona has been unfaithful.
His understanding of the human psyche is phenomenal, as is his ability to orchestrate a complicated interweaving of pre-planned scenarios. Iago's deception is potent because of his patience, his cleverness, and what seems to be his intrinsic love of elegant manipulation. Dude's a bit of a sociopath if you ask Shmoop. He's almost too good at playing people.
The truth is: he manipulates Othello by weaving an elaborate and brilliant web of subtle lies and suggestions. He doesn't come right out and say Desdemona is cheating. He leaves that part to Othello. He knows the lie will be even more effective if Othello comes up with it himself.
This phrase might be said in response to Cassio's (supposed) dream, but it really describes Iago's entire scheme against Othello. He lets Othello believe everything is a foregone conclusion, when really nothing is.