The only rigorous method, the only one that enables us to
test an opinion against reality, is based on the clear recognition
that opinions come first[as opposed to facts]—and that this is the way it should be.
Then no one can fail to see that we start out with untested
hypotheses—in decision-making as in science the only starting
point. We know what to do with hypotheses—one does not
argue them; one tests them. One finds out which hypotheses are
tenable, and therefore worthy of serious consideration, and
which are eliminated by the first test against observable experience.
-- Peter Drucker The Effective Executive
So what about MWI?