It could be, for example, the risk of a change in the economic environment - what are your contingency plans for that in terms of dealing with such a situation? There may be many other risks as well specific to your particular sphere of operation, but that ability to plan ahead for all scenarios makes for a robust business plan.
Everything on earth is tending to become compact. Gone are those days when a sea beach was described in a thousand words. Today, a similar description is possible with a powerful visual and a string of strong adjectives in only a few words.
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.
Most of all if you are seeking funding for your business, it will be absolutely crucial to go along and show someone an actual plan, because there will be very few people who will loan you money on the basis of what's just in your head. So it's pivotal to have a plan and be committed to preparing that document.