Do you have a Plan B? A contingency plan. Should you? The fact is that most people don’t even have a plan A.
You don’t need to prepare for every possible scenario as long as the problem has an easy solution. For instance, Rick Steves says not to take headache medicine with you on a trip “just in case” if it could be easily acquired at a drug store where you’re going. This might sound contradictory with the recommendation that you have a backup plan, a Plan B, but it’s not. The backup plan is to go buy what you need if the situation arises.