|Paul (27 Feb 2017 21:36): The most obvious blame to cast is on Brian Cullinan, who tweeted a picture of Emma Stone minutes before the mistake. However, the key to robust systems is redundancy---if you can identify a single point of failure, it means the system wasn't robust in the first place.|
You can blame the miscommunication between Beatty and Dunaway---maybe he could have said, "I just want to be certain this is the right card" rather than show her the card and hope she'd also scrutinize it.
But I really want to find a key point of failure that isn't just human error at the moment. So I'm going to blame: the card design!
Yes, that's the same thing many people blamed for Steve Harvey's Miss Universe gaffe.
I really think the lesson apparently not learned from that one is that the card should show the exact sentence the announcer should say.
In this case the mistake card says, "Emma Stone / La La Land". If only the card had said the whole sentence, "The award for... Best Actress in a Leading Role... goes to... Emma Stone ... in ... La La Land" then the mistake would have been clarified before it was announced.