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.
Marketing Plan: Marketing plan lays down the strategies of marketing which can lead to the success of business. These strategies are in terms of marketing mix (product, price, place and promotion). From the market feasibility study and marketing research, potential/ present demands of customers are determined which helps in understanding the profile of customers and hence help in laying down the strategies for segmentation of the market, identification of the target market laying down strategies for target market.
It is known to be the most crucial step in the successful running of the business because a well planned business venture carefully scans all the possible opportunities and threats, understand the demands of the market and arranges for the best possible resources which finally lead to the success of the business.
I say that because of course you need to be careful with commercially sensitive ideas, as you do not want to pass your plan on to someone in the pub who then starts your idea before you across the road.