Plan B is what you pivot to when you recognize that a new opportunity has more potential than the one you are working on. Sometimes you change to Plan B because A is not working, which is what most think when they hear “Plan B.” But sometimes A is working, yet Plan B appears to have more potential. Regardless of the reason for shifting, the best Plan B’s are different but related to what you are doing now; this way you can apply the lessons you’ve learned to date to the new plan.

This is right on. It's not necessary that Plan A was not going to work, but it's that you recognize a bigger opportunity in plan B.