Ken Gullette (1) A force of four ounces

From the sentence "A force of four ounces deflects a thousand pounds," we know that the technique is not accomplished with strength.

Reference:  THE TREATISE ON T'AI CHI CH'UAN | Attributed to Wang Tsung-yueh [Wang Zongyue] (18th Century) | as researched by Lee N. Scheele.

Ken Gullette is absolutely right:  Once you have sufficient mastery of T'ai Chi and self defense applications, you don't have to do much to respond to an attack.  Minimal energy, minimal effort, just a slight turn of the body and a shift in weight, and you're in a positive of advantage.
 

How T'ai Chi is Healthy (3) Lifting

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T'ai Chi practice looks deceptively soft and easy, gentle and light, and well it should appear so to a casual observer.  But in reality it is heavy and rooted, that is, keeping the body weight underside.  So moving the arms and legs, for example, requires some lifting, in ways similar to lifting weights in the gym.  More specifically, it's not an exercise where we put on medium to heavy weights on the barbell or machine and where therefore we can only do, say, 8 - 10 repetitions.  Rather, it's an exercise where we work with light weights, which we lift via very slow movements and we perform for several  repetitions.

How T'ai Chi is Healthy (2) Stretching

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T'ai Chi practice is one stretch after another:  from arm reaches and leg extensions (kicks), to Fair Lady Works at Shuttles and Snakes Creeps Down.  Its form - I practice mainly the Yang Long Form - is a gentle, continuous stretch, which is precisely how to do it: not tense or bouncing, but extending in a relaxed, centered manner.  As I (we) get older, staying flexible and limber are a key to managing properly whatever small or large physical demands we face.
 

How T'ai Chi is Healthy (1) Balancing

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T'ai Chi practice works at rooting and centering our bodies throughout the movement, while keeping mindful and relaxed (sung).  There is no way to ensure that we keep our balance, when something knocks us over or when we slip on the pavement.  But the agility and steadiness that T'ai Chi engenders reduces the likelihood that we will fall over or get injured when we do.

How T'ai Chi is Spiritual (3) Connecting with God

Creación de Adán, Miguel Ángel (c. 1512)

More than just feeling the essence of God within me, T'ai Chi study and practice connects me, I'd like to believe, with God Himself.  Much of its movements are expressed via the hands, and its chi is release through the fingertips.  So this peerless masterpiece by Michelangelo, in which God breathes life into Adam as the first man, is a perfect rendering of what I believe to be the larger purpose of T'ai Chi.
 

How T'ai Chi is Spiritual (2) Much Bigger Than I

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Some of us may resist the notion that we are merely drops of water in a vast ocean.  Some of us, in other words, may see themselves as bigger than they actually are.  But in truth there is a vast cosmos around us, and T'ai Chi practice lets me get in touch with that which is much bigger than I am.  In T'ai Chi, we simply refer to the vast cosmos as the Universal. 

How T'ai Chi is Spiritual (1) Non-Physical Self

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T'ai Chi practice lets me get in touch with that part of myself that is non-physical or non-material.

• Is thought a non-physical phenomenon?  Some may argue that it is merely neurocognitive activity.  
• Is emotional a non-physical phenomenon?  Some may argue that this, too, is a biochemical, anatomical event? 
• What about chi?  Some define it as breath, which of course is physical. But more accurately defined as life energy, it may be an arc toward our spiritual self.
• What about shen?  Meant in the sense of awareness or consciousness, shen may be the essence of God that courses through us.

In T'ai Chi practice, we say sink the chi, raise the shen.  One ought to circulate in our body, while the other reaches upward and lifts us along with it.