If an opponent's knee had been in the way, it would have been broken. Here, in practice, my foot hangs in midair for a beat, twisted slightly to put the edge of the foot toward the target, the big toe pulled upwards to help with the form. I withdraw the foot and step down, with control. In a real fight, you might jump into this kick, stamping downward with all your body weight concentrating into your opponent's knee, breaking the complex and fragile joint easily, tearing ligaments asunder, rending tendons from their bony anchors.
That's why I'm not sure I should be here. Would I ever really want to do that? To commit someone to hospital, to traction or surgery or endless sessions of physiotherapy? I've had knee injuries. Once I came off a snowboard and smashed a knee into a carelessly-placed Alp at high speed. It wasn't a good experience. I was limping for weeks, and still having a therapist treat the haematoma with tickling ultrasound months later. Would I be prepared to inflict this on someone else, deliberately?
So my form was not good, and my kick was unconvincing, and my sensei raised a small wiry eyebrow, which was all he needed to say.
My next sokuto fumikomi, the side-stamping kick to the knee, was from from hidari hanmi gamai, the left fighting stance, and was much better.