Sun Tzu wrote, Now an army may be likened to water, for just as flowing water avoids the heights and hastens to the lowlands, so an army avoids strengths and strikes weakness. It is sufficient to estimate the enemy situation correctly and to concentrate your strength to capture his. There is not more to it than this. He who lacks foresight and underestimates his enemy will surely be captured by him. In summary, what Sun Tzu is saying is that you should know your enemy. He emphasizes making quick assessments of the enemy and developing tactics and strategies to meet the need.
On a person-to-person level these precepts are linked and quite basic. The opponent must be sized up quickly. Is he or she taller or shorter than you? Does the opponent appear weaker or stronger? Is the person armed? Is the person heavier? These assessments must be made quickly and reactions must be made accordingly in order to prevail.
A stronger opponent would more readily be defeated through attacks to the groin and knees. To take the advantage of reach away from a taller opponent requires bringing the fight close to that person - closing distance quickly and using elbow smashes and palm heel strikes to key target areas. These are just some examples. Deshi should train bunkai often and with people of various sizes, weights and skills. Training should be done at various speeds to work on targeting (half speed) and reaction time (full speed). In addition, bunkai should be worked on for all the kata that a deshi knows so as to practice the full range of techniques with varying opponents. Repetition is also key, as only through repeated practice of techniques through bunkai will a level of proficiency develop that will give the deshi confidence that the technique will be there for them should the need arise. One final, but no less important point, Hanshi has always stressed that we develop a handful of techniques that are our own or our individual go to techniques that we would use in a situation. The practice of bunkai will provide the student with a good sense of what techniques are best for them.