When you, and your partners if any, have all the core skills and industry knowledge you need to start right away without seeking experts, napkin notes may be enough to get going. Let's say you are already an expert in technology and social media. Then you, and your team, probably don't need a detailed plan to start developing a new app. You will draw on your knowledge and experience, and you understand that you might need to go back and do some more detailed and formal planning later. Certainly when you reach the point where you are looking for investors or lenders, you will move beyond those first casual notes. Until then, drawing upon your expertise can allow you to quickly jump into the market and perhaps gain a competitive edge by using a minimalist plan.
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.