An important thing to keep in mind is that it's not that you are innately incapable of answering the question, you just may not be able to do so presently, whic

An important thing to keep in mind is that it's not that you are innately incapable of answering the question, you just may not be able to do so presently, which is why it's a great question. People who are in a rut, or carrying a lot of baggage, (among others) are going to have trouble answering it, and they're probably also going to have trouble adjusting to a new position. Not to say that you are, but it would register as a possibility to an observant interviewer. People who are currently active and engaged will not have trouble coming up with something, and they probably won't have trouble getting their point across in 5 minutes. You might actually have trouble stopping them after 5 minutes because you're engaged with what they're talking about. This is a good sign of someone who wants, and is ready for a new opportunity. That said, I've used slightly constrained versions of this in interviews, like picking up on a side comment/complaint someone made early in the interview. It's a good way to really see someone hunker down and think and express themselves without putting them on the spot like a test. Note that you inserted the idea of the "best concept" on your own, you've made it into a test which implies a right answer, when it isn't. Things like that are warning signs when it comes to adding a new personality to a creative team, and why this style of question is so revealing.