I think this was pretty much the topic of one of his books

Mother Night: "We are what we pretend to be, so we must be careful about what we pretend to be."

Heh I didn't know that. I heard/read the quote from Sivers.

"Fake it till you make it" meme?

It was used in a similar, but twisted, sense in the book.

In the book, Mother Night, the character is working for the US (and the Allies) but under the cover of working for the Nazis. So it's a bit of a twist on "fake it til you make it". In the latter, you pretend to be what you want to be. In the book he's pretending to be what he doesn't want to be, but the consequence is that post-war he's perceived to have been a Nazi (or at least a collaborator).

And arguably, was.