Very true. When doing business if you allow in your thinking there will be problems, you will handle them much better.
You have to have a "plan" to deal with the normal and typical problems without letitng yourself go negative. It's a tough balance to maintain at times.
There´s a saying that I learned while working as a producer for TV: "Fail to plan, plan to fail!" I think that should be applicable to every kind of job. Think of all the possibilities of what can happen, and of the solution to the possible problems.