But do not be too paranoid, make sure you are showing it to people you trust, whose feedback you welcome and can be genuinely useful in guiding how the plan takes shape. Very often when working as individuals we get very close to certain details and miss out a big thing that has slipped your mind. You can concentrate so much on essential financials and supply logistics, but overlook other issues like marketing or opening times. By showing the plan to someone you trust, they can have a look and see what might be missing or worth developing more. Getting that valuable second opinion on how robust your idea is will put you in a much better position to start and keep going successfully.
Now as I said, there are many other reasons too. After graduating from college, I started out in manufacturing as an engineer in a pretty large company and now, 45 years later, retiring as a of Director of Manufacturing, I have discovered an awful lot about business. Not only did I learn and teach a lot about business, I worked with small business owners as well. I've learned that it comes down to this. Too many owners work hard in their business but less on their business.