We can never be prepared for EVERYTHING that happens but we can plan for what you assume could happen.
The method and action of creating a plan are more valuable than the plan itself because of what it instills in you. There is a feeling of confidence, excitement, and peace that comes from planning. The plan itself is just the end result of the act of planning.
The preparation that comes from planning is what allows you to take on any unexpected outcome better whereas the plan itself can, and usually gets thrown out the window as soon as a surprise comes your way.