You can plan for what you know, but you can’t plan for the curveballs that are inevitably thrown at you.
Being able to follow a plan is half of what is needed to take a day in stride; the ability to respond without preparation to a plan being derailed or diverted is the other.
There is no degree, course, or instruction manual that will tell you how you should respond to sudden changes.
All you can really do is believe in your ability to find a way forward.
And though that won’t be enough in every circumstance, it will be in many.