What if I don't believe in the company I'm now leading?

You set the story for the whole company, and quietly you are not sure you still believe it. That is a hard place to stand, telling a tale you have started to doubt. But notice that you are asking the question at all. A true cynic would have stopped caring whether it was true long ago. Belief is not all or nothing. You can doubt parts of the machine and still find something real worth telling. The task is to separate the honest core from the hype you have been layering on. What does your product actually do for a real person on a normal day? If you can find one true thing there, you have something you can stand behind without pretending. So go find it. Talk to one customer this week who genuinely benefits, and listen. Build the next story from that truth outward. If you look hard and find nothing real to believe in, that is worth knowing too — but do not decide that until you have honestly looked.