luck seems to be with iago in his schemes what stroke of fortune from iagos point of view lends further credence to his lies about cassio and desdemona as othello watches

It is a stroke of fortune for Iago that Bianca arrives just in time to hand him the handerchief that damns Desdemona. It makes no difference that she gives Iago the token because she wants nothing further to do with his plans.... the handkerchief's presence in the room says exactly what Iago wants Othello to hear.