The Noble Art of Keeping Your Balance Standing on One Leg
In Yoga exercises standing on one leg is often used to train both physical and mental balance. In tai chi standing on one leg is part of a movement, e.g. a kick, but if done slowly it still puts demands on your ability to keep your balance, and it is a difficult point for many who want to learn the form.
It is important to understand that you are not attempting to keep your balance standing on a single point. The foot sole is not so small after all, and toes and heel make it unlikely that you fall over to the front or the back. Chances are that you will lose your balance to the inside towards the foot that has left the ground - maybe because you mentally have prepared for it to save you if you lose balance. So standing on one foot dare to transfer all your weight to it. You might imagine that you are wearing a kind of football boots with at least 4 studs placed as a rectangular pattern under them to emphasise the surface of the sole.
Over the grounded foot the whole body must be aligned, but not in a rigid, inflexible way, and if you do not feel as one whole and conscious organism the surface of the sole will not save you. If your body seems to consist of unrelated building blocks without a centre and a centreline you will not know when you find or lose your balance.
Learning tai chi you will experience that some days are better than others because of the way you feel your body and soul. Accept it and practice to become more balanced.