Good point jpaynecr. Very good point. But other variables happen as well, but financial is the major factor for loss of business sustainability.
But, it is not essential to follow a business plan exactly. Or at least, re-define or modify your business plan periodically (such as every 5 years) to adjust to the changes. In the beginning, business plans are safest, but in the long run, th business plan on paper itself is either forgotten or nothing like the original due to changes in the company and time (such as acquisitions, diversification of product/services, new accounting/financing style or practices, etc.).
Keep a strong financial head on your shoulders BP or no BP.
Also, keep in mind investors are not the same. Some are focus on different aspects of a proposal than the other. Angel investors, for example, may be less critical of the details of an outlined financial plan (other than projections and payment practices) and focusing more on the marketability and personality/mind of the proposer(s). Especially since angel investors have less control of finances and have a more flexible grace period for ROI. Venture capitalists and banks are the serious cats that you have to sell numbers to. (I say 'sell numbers' since thats what u're basically doing...saying this is how we plan to give u the best ROI we can offer, and here's all the hoopla analysis and charts and all those boring details that u think are pretty....eat it and love it).
But after u make the BP, if u do, and get the capital u ask for or is necessary u might as well throw it away because all of that has to be in the mind of u and ur team anywayz.
Just my opinion anywayz.
www.smallbusinessplanguide.com is a resource I just found on Google. Good luck!