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. While I still recommend the business planning process, I caution you to realize that a beautifully crafted document does not always equal business success. I've worked with many entrepreneurs who successfully launched without a plan, and some with beautifully written plans that never materialized. You and your business idea are unique. Your planning process will be unique as well. Be wary of one_size_fits_all advice or pronouncements from experts about how you should proceed.
A business plan is essential for all businesses regardless of size, and once one has been written it is also important to maintain and update said plan. That being said, it is important to realize that whilst writing a detailed plan is useful and a good foundation for any successful business, it will not necessarily make the business a success or guard you from all disasters. If you keep up to date with business plan it will prove a really useful tool throughout the lifespan of your business. However, if you grossly over exaggerate profit margins or your budget then your business plan could also lead to failure. Stick to the figures and be realistic and your plan should hold you in good stead in the turbulent business market.