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.
At this point, you may be tempted to skip writing a business plan altogether, viewing it as an unnecessary exercise in jumping_through_the_hoops, suggested by some old business professor who probably never held down a "real" job anyway. Maybe it's okay as an assignment for an MBA class, but it would be just too confining and irrelevant for today's fast_paced business environment. Anyway, you're ready! You've thought about this business venture for a long time and talked it over with friends and everybody agrees it's a great idea. Best to strike while the iron is hot!