you and you both go crashing to the ground because you lack the stability and structure to stay on your feet and then you're off looking for something else to cross-train in (unless you've already done that) to get that and maybe still wondering how O'sensei was able to do what he did while really only training in one thing... ymmv
OSensei trained many different arts. The fundamentals of any art should teach you balance and stability. The one off situations or maybe they are more common than that....where someone falls into you or perhaps you put your foot down wrong and you go down. That is part of "combat" if you will. That is where you hope your training has taught you how to overcome the unexpected or unintended.