As a matter of fact, did you know that the Small Business Administration says that 50% of small business owners will fail sometime during their first 5 years? There are lots of reasons but one big one is that owners don't have a plan. Another is they have picked a product or service that doesn't have a big enough market to sustain their business and sometime during their future they will run out of customers.
Location: Writing down the location of your business is very important. Locations with greater customer traffic usually cost more to buy or rent, but they require less spending for advertising to attract customers. This is especially true of retail businesses where traffic count and accessibility are critical. If an online business, you need to go into detail how you will attract customers to your website. General statements like "I will use Face Book ads and email marketing" will contribute almost nothing to helping your cause unless you have detailed statistical analysis of tests you have conducted or of another similar business you have been associated with. If you do not have any data upon which you reference your estimates, it could show lack of proper thought to the remainder of your business plan.