Magic is what it is and showmanship is the goal. In magic misdirection is a primary tool of the magician. Telling you to watch this hand while the other does something you are not aware of is a fundamental magic act.
You are told the greatest martial artist of all time is going to be at a tournament to demonstrate his art and you are already primed to beleive what ever is provided for entertainment when you get there. No one, especially Bruce Lee, wants to disappoint the audience - right? You are now predisposed to associate your expectations toward what you have perceived from other legendary stories that get around.
Next misdirection, your told that he is going to demonstrate the one-inch punch. He shows you his fist and then moves it into position while tapping it on the uke's chest where it will land. Your eyes are going to remain focused on that fist and hand so that you will not direct your awareness to the actual specifications that make the magical act work.
Take a look at the film again and ignore the fist entirely (note: one reason this worked so well was Bruce Lee's speed and economical motion; he had the principles of martial systems down - pat!). Go through it a few times and make note of the various parts of Bruce Lee's body. Things you may notice, his lead foot rises off the ground a bit; his body starts to move forward slightly; his body will lean a bit; his lead foot will not step down in a slightly forward motion along with the forward motion of his body. The hand and arm will flex forward slightly, the one-inch move that says this is a one-inch punch.
The fist seems to move only an inch by itself because the audience has been told to watch the fist/hand - not directly but by misdirection when he shows the hand, moves it to the target and then you remain focused on it during the actual event.
Now, take the same time and look at the uke. Look at the stance, the legs and the position of the feet. He is standing loosely in heiko-dachi facing directly forward to Bruce Lee. This is the absolutely worse stance to take in this situation for maintaining balance, etc.
Lets review an old post on stances, "Stance Effectiveness."
|Graphic created from Marc MacYoung's book on martial systems.|
The stance integrity for the uke is allow maximum ability to unbalance because the integrity line of the uke is the weakest from the direction of force applied vs., if he had taken a side stance with an integrity zone creating the greatest stability of the stance used. You can get the idea from the graphic in that post linked above.
As can be seen with analysis you begin to see a chain of traits and specifications that would promote maximum effect of the event to gain the greatest amount of entertainment and awe inspired showmanship. You can literally stand in front of the uke and use one finger to unbalance him. This stance allows Bruce Lee to actually use the old boxer technique of falling forward with a drop step to create power from the forward moving body mass into the fist.
The fist is not the delivery of that force but merely the conduit of the force as it travels along the path to that fist and into the uke.
Ok, all said and done so I want to express that this analysis is not to through disparaging remarks against Bruce Lee. Bruce Lee is a great martial artist and has accomplished great things in the martial world as well as in the movie entertainment world. I was inspired by him as a youth when I first say the "fists of fury" b-style flick. Really cool and I have not seen anyone who has mastered the moves he did then and now - some are very, very close but ....