Because I am a huge George Lucas fan, I will relate some of the concepts to you in the context of Star Wars.   "A New Hope" began with, Ben Kenobi telling Luke that the Force is an energy field and their source of power.  I imagine ki to be similar in the respect that it is also an energy that flows through us and is a source of power.  I have heard many stories of people generating unbelievable strength in survival situations.  If asked to do this in our everyday lives most would agree that the goals are unattainable. Ki training is an attempt to harness this huge source of power as we practice the art.  We in Aikido believe that ki originates our center, or One Point, which is our center of mass.  "Extend Ki" is one of the Four Basic Principles of Aikido and signifies the projection of this power.  Aikido techniques focus on blending with and redirecting the ki of our partners to achieve control or neutralization. 

One of the ways Aikido techniques illustrate the power of ki extension is through the development and testing of the unbendable arm. In the attached video, Tohei-Sensei demonstrates unbendable arm, unliftable body, and a few other examples of the power of ki extension. Standing in a well-balanced posture with an arm extended in a relaxed manner you imagine that your center is the reservoir for a vast ocean of water, which can be "directed" by your mind to flow out your extended arm as if to put out an imaginary fire against the wall. You will find that it will be more difficult to bend your arm in this situation than if you were trying to hold it straight with conscious strength. It is analogous to a fire hose, which is supple and bendable when not full of water (in fact it is made ready to use by the firefighters by folding the hose upon itself). However, once the hose is "charged" with water from a hydrant, it becomes so stiff that it will not distort even if one drives a car over it.

Overcoming an adversary is easy if you are bigger, and stronger, but much more challenging if you are on the other end of that equation.   Women may be considered to be at a disadvantage when confronted by a male of the same approximate height and weight because the male normally will have greater upper body strength.  Utilizing the power of ki extension along with proper body movement can help to overcome this apparent advantage, which is why women tend to internalize these principles earlier than men.  The principle is the same when a smaller man practices with a larger, stronger man.  Conclusion:  Ki flows through all of us.  Training in Aikido helps us to develop and potentially harness the power extension resulting in less reliance on conscious physical strength to overcome the power of a given attack.