If you need to get going quickly to ride the wave of a fad before it fizzles, then fast, bare_bones planning may be all you've got time to execute. This works best when you've already got the infrastructure in place, perhaps from previous projects or an established business, and you can simply shift energy and resources to the new idea.
Look at the assumptions you baked into your original plan. Did the city follow through on opening that new park across from your location? Were insurance rates what you expected? How many hours of accounting or web design help did you really need? Are your online inquiries out_stripping your face_to_face sales? Or vice versa? Sometimes no matter how much you research, plan, or test, things don't go as expected in a business. This isn't necessarily a herald of failure or a sign that you're not cut out for entrepreneurship. Life and the marketplace are both unpredictable, and plans need to be fluid and responsive. The "One Pressing Issue Plan" is simply a reflection of a normal evaluation process.