I completely agree with you that while making your business plan, there should be provisions for unforseen outcomes. In other words, extra capital should be kept and a back up plan should be in place in case things do not go as planned. But you would agree with me that it is impossible to actually make preparations for every possible outcome in a business venture.I strongly believe risk taking and failures be included in every business plan.
Without analysing the WHOT of the business you intend starting up, you may be taken off guard.
In a case where problems arise, carefully planned measures can be taken if the problem was already foresighted.