I cannot tell if this is rationality or anti-rationality:
Q: What is Microsoft's plan if Windows 8 doesn't take off?
A: You know, Windows 8 is going to do great.
Q: No doubt at all?
A: I'm not paid to have doubts. (Laughs.) I don't have any. It's a fantastic product. ...
I'd saying telling an interviewer you have sufficient confidence in your product to not need a backup plan is rational, actually not having one isn't.
Here's the new thread for posting quotes, with the usual rules: