In the video below, a very excellent, accomplished, powerful and much respected martial arts teacher and author brings up a very interesting question about the Zheng Manqing Tai Chi form's unique hand shaping, the softly extended fingers with flat wrist called 'Fair Lady's Hand' (美人手).
His physical demonstration of the contrasting shapes involved is perfect.
However, the analysis needs more nuance. It is slightly backwards:
"Cheng Manching's rationale for this was, well, most people's hands are just too tense to be able to bend them back."
That is a mistaken view of CMC's rationale. In fact he knew perfectly well that anybody can bend their hand back. As BKF says in the video, ALL the Yang students bent their hands back, presumably from their first class onward. So how could CMC possibly have thought that "most people's hand are too tense TO BE ABLE to bend them back" ?
Clearly it's not a question about physical ability. Any normal human being (who is not totally arthritic/sclerotic) can bend his or her hand back, no problem. CMC's rationale may seem at first glance like the above italicized statement, but is in fact different, it's much more subtle, and the truth of it is also personally verifiable. It's something Ben Lo often had people test when (umpteen zillions of seminar attendees) had asked him about this very same point. Ben Lo would simply say (quoting CMC, who had given this same demonstrative answer when Ben Lo himself had asked this same thing - there's no end to it all... )
Ben would tell the questioner:
"Bend your wrist back. Good. Now look at your hand, and feel your hand, remember the look and feeling. Got that? OK, now, form Beautiful Lady's Hand. Look at your hand. Feel it. Got that? OK now compare the two conditions - which is more relaxed?"
That's all. People (even most professional Tai Chi teachers and authors) are so unbelievably tense - without even realizing it - that Yang Cheng Fu created and transmitted to CMC this small but potent method of both:
(a) helping to make us aware of our tension; and
(b) helping us to actually eliminate it.
The first principle of Tai Chi is "relax". Anything that is demonstrably more relaxed (while keeping conscious mind in the game, not collapsing) is a priori superior to something less relaxed. When you have learned to make all your tons of unconscious tension conscious, and then learned to drop it at will, then and only then you can shape your hand any damn way you please.
(It's also true that - under certain crucial and specific conditions of awareness - a physical extension of the daling point at the inner wrist can complete the full body energy circuit. However, most people who are bending their hands in Tai Chi are of course very far from even the remotest understanding or experience of that. For details please refer to my book The Aiki Singularity).