1. Basic Principle of the Theorem
It appears that we are more stable if we stand with both legs rather than with one leg.
Taiji lays importance on balancing oneself in action but it would appear that its Theorem Against Double Bases ("TADB") is at odd with what we normally think about balancing. According to TADB, a double based position is a bad position.
Why single based?
Look at the top in the picture above.
The foot of a top is small. It will fall down easily when it is static. However, a top will not fall down whilst spinning.
To name one obvious advantage: A spinning object generates centripetal force or centrifugal force.
A double based object cannot spin around easily. Likewise, a doubled based person will not be able to spin his body easily in action - he can only do so by putting all his weight on one leg.
In order to overcome the Strong Man Principle, a weaker party has to move around quickly and deal with the stronger opponent with suitable techniques.
Not knowing the secret of the TADB, a double based party will ironically, and inevitably, end up locking horns with his opponent!
2. Moving Forward
At the beginning of the taiji martial art training, a practitioner learns how to maintain his balance. At the later stage of the training, it is the reverse. A senior practitioner should learn how to make use of the force generated by the lose of balance. This is not a situation of really losing one's balance. The unbalanced position is somewhat "intentional" by making use of the TADB. It is "created" as a result of "sticking, adhering, connecting and following" to an opponent to such an extreme that one can no longer maintain his balance.
A skillful practitioner can, however, make use of the power produced by such an "unbalanced" position to uproot his opponent and, through uprooting the opponent, maintain his balance again - he is now in a recovery mode. It's just like holding the hand rail in a moving train to maintain one's balance. The power as generated by an unbalanced body is not enough to move a train, but it is more than sufficient to uproot an opponent.
This is the conversion of balance and unbalance, the conversion of Yin and Yang.