Same guy who proudfully and ignorantly kept his back to his apprentice while he tried murder his son infront of his eyes in cold blood. Yup, the guy really wouldn't make any mistakes like that... Oh wait.... Palpatine's greatest character weakness is his overconfidence and pride. Both are made painfully well known to the audience. It is not unreasonable to assume the guy has made more than one life altering mistake. I get that people don;t want Plagueis, but when they come at it form the angle that Palpatine cannot be capable of making mistakes that huge... Well, have you watched RotJ?