People like that are easy to manipulate. So it's all decided. I've worked it out.
Iago thinks that it will be easy manipulate Othello because he married Desdemona.
Othello would talk to Desdemona's father about his childhood and Desdemona would listen to every detail Othello would say. When Desdemona would miss a part of Othello's story she would go sit with Othello and ask him for the rest of the story.
Othello was getting peer pressure when he was deciding how to kill Desdemona. He was getting peer pressure because he didn't know if to strangle Desdemona or if to poison her.