Your tactical plan is really a set of plans, or options, if you will, from which you can draw during the competition to cope with whatever situation presents itself to you. You need to anticipate any number of situations which may arise during the competition, and have one or more options at the ready to apply in the given situation. You can never anticipate all the situations which will confront you, nor should you limit yourself to the options you have developed in advance. However, having considered several possible situations, you are more likely to make a good choice or to create a positive new solution. You can control your state of mind.
Uncertainty leads to fear, fear leads to tension, tension leads to . . .
You must be relaxed mentally to be relaxed physically, and you must be relaxed physically in order to perform your best. So you're equal. Next, but equally important is to know the course. If you're running on a 400m track, this can be of less importance, but if you are running on a road course or a trail, knowing the course well can mean a tremendous improvement in your performance. You should also give yourself some landmarks along the way, where you want to implement certain elements of your strategic and tactical plan.