You get into a room with a bunch of key execs who are not part of your project and then they tear your product/movie/idea apart.
You don’t have to implement any of their suggestions but since these are seasoned execs they see flaws readily.
The key is that the process encourages candid feedback without hierarchy or defensiveness.
This goes on for a couple of iterations until the idea is ready for production.
I think Apple has something similar.