It's like planning backwards. 1. Determine what you want in life 2. Figure out what your business would need to do to give you that life. 3. Figure out how long it would take you to reach it. 4. Figure out how big of a market it would take each of the years you're planning for. 5. Then see if that market is big enough. Isn't this a much better way to go about planning your business? Shouldn't your business be designed to give you want you want instead of you working yourself to death just hoping for the best?
I have written business plans for all manner of industries: a coin operated jukebox company, airlines, travel companies, new product launches, and anti_aging product companies. It is not necessary to have a passion for the product or the company to write or develop a business plan. What you must have is a passion for aggregating information, getting involved with and understanding the service or product, and understanding the financials of the product or service. By financials I am not referring to having a CPA before you undertake the task, but rather understanding the presentation of the information and analysis/ numbers to support the activity being planned. Financials are important because they are the score card in the world of commerce.