On sincerity and narrative

David Thomson in The Guardian today poses an interesting question. Apropos of a discussion about how, excepting Alfie and Get Carter, Michael Caine only ever plays Michael Caine (which is, I think, wrong by the way), Thomson says:

Sincerity is vanishing, and I'm not sure that narrative can survive without it.

I'm not sure what to think about this. At one level it's saying that there must be truth to make any plot believable. Sure. But then, what we're talking about is the superior sort of lie anyway, so are we saying that if we put too many quote marks around things, we can't actually get any forward momentum from beginning to end?

Any thoughts?