I responded online as follows:
Both Aaker and Ries still agree about the “one idea” that encompasses the brand. I used to be a diehard Ries acolyte but there are too many cases where brand extension works – at least for the short term. And really, in some business models, the short-term is all that’s required.
Some brands in fact, are too powerfully associated with a particular concept and fail utterly when that concept is paradigm shifted out of existence. Polaroid is a good example. Instant prints. Their failure to move aggressively into other spaces tied themselves to instant prints forever. Now they are a one-trick pony consumer brand and just a shadow of their former size.
It’s sort of like the actor who’s only known for playing gangsters. They get typecast. Sometimes it takes a major shakeup to move beyond the typecasting.