Given less than perfect information as the norm, running a business is about making assumptions, taking action, and monitoring your results, then adjusting your assumptions and starting the whole cycle over. What tends to happen instead is that an entrepreneur puts together a business and/or marketing plan making a lot of assumptions. Then he/she gets so busy building and running the business day-to-day, that he/she puts the plan in a drawer and never looks at it again. Don’t make this mistake. Make sure you have a good understanding of your key assumptions and monitor them against reality on an ongoing basis, not just once. This mentality of testing and re-testing everything should permeate every operational aspect of your business.