The people who build successful businesses are by and large optimists. If they weren't, they wouldn't have the commitment and the drive to invest so much of themselves and to build a successful business against all odds.
I am all in favor of optimism, and a positive outlook. If you believe that the sun will come out tomorrow and likely it will!
But in business transactions, as in life, allow for the possibility that everything won't go according to plan.
Be sure that your plans address both the probability that everything will go smoothly, and the possibility that there will be one or more unexpected glitches that will need to be identified and resolved.
Experience is the only solution in preparing for unexpected complications. When you've been through the process over and again, you learn to solve even the most unforeseeable problems.
For example, if you went to the hospital to have an ablation performed to address your atrial fibrillation, you would definitely do your research to get the cardiologist with the maximum amount of relevant experience in your corner. In all likelihood, the procedure should go as planned. But if the unexpected happens, you want the cardiologist with the most experience addressing any complications that can crop up.
It is for the same reason that you want a transactional attorney with a breadth of experience in your corner the next time you contemplate a business transaction, be it an acquisition, a disposition or a joint venture.