Inexperienced entrepreneurs create a business or product without knowing who their potential market audience is going to be. They innovate some new service and/or product and then go find the market (people to sell it to). If your goal is to be an entrepreneur (as opposed to an inventor where this model is part of the process) this course of action is ill-advised.
Seasoned entrepreneurs seek out hungry customers with a problem and then try to provide a desirable, consumable solution (product or service) to help these people alleviate their problem. The potential and capacity of your entrepreneurial reward is determined the minute you finalize the market choice for your product or service.
The world’s most successful fishermen will tell you this piece of advice (which is just as applicable to starting a business): You can have the best fishing pole and the best bait and still not catch any fish in a puddle of mud. With the advent of the Internet, there are some great ways to find a profitable market before you get started. A great book covering the topic of AdWords (with lots of details on finding profitable markets) is Google AdWords For Dummies by Howie Jacobson of AskHowie.com.
