This is the most difficult area of technique. It requires good timing as well as sensitivity to the attacker's movements and intent as well as a good deal of knowledge of the anatomy of the various joints and "stuf like that". However when done right, very little strength is needed because you isolate the body part being attacked, placing the other into a position where they cannot use their strength to resist you, taking advantage of their reflexive reactions and the weak spots in the design.
One of the ways we teach the idea that physical strength is not the "trump card" is thru our practice of groundfighting. At first, especailly the young men, will try to muscle through everything. Watching two of them go at makes me tired! But eventaully they notice that the older studetns(male and female) are beating them without doing that, by staying relaxed and fluid.
When it comes ot kempo techniques, it just takes hands-on instruction, if I see a student trying to muscle thorugh something that should be "finesse", then they get corrected... as many times as it takes