What should come into your business plan is how you assess it, how you foresee anything occurring that could have an adverse impact and how you would deal with it in the right ways. If you are looking to obtain funding from a bank or people you know, it is essential to show what the risk factors are in the proposed business and how you plan to defend against them.
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. When I have received business plans, the very best responses come from people who have looked at the risks and have an answer for every question. What you never want is to throw a scenario at your plan and have to answer "I don't know what I would do in that situation". You want to plan for every possible contingency, and certainly all the major risks to the ongoing success of your business.