When first learning randori no kata (the 17/23), I sort of misunderstood what I was really doing. I looked at each technique as individual things, doing individual jobs, different jobs. With shomen ate, I was attacking his face; with kote gaeshi, I was twisting up his wrist in an uncomfortable way; with waki gatame, I was locking up the elbow, and so on.
I also tended to focus more on what my hands were doing, rather than what my center was doing. (I suppose all this might be what's referred to as omote, what is seen from the outside, or on the surface, and the reality of the matter being the ura, the hidden or maybe not-so-obvious truth).
Then, one day (and this probably took longer than it should have) I finally realized that I'm not attacking unique, separate parts of uke's body, but rather I'm always looking to disrupt uke's center line, and consequently his balance, and his effectiveness to attack me. I'm also doing it with my center, the energy just happens to be transmitted through my arms.
Suddenly, the 17 started to make a little more sense. With the first 5 (ateme waza), we're going after the center line directly; with 6-10 (hiji waza) we've moved further away and are now affecting the center line but now through uke's elbow; the next set 11-14 (tekubi waza) we've moved even further away and are affecting the center line by way of their wrist.
The last 3 (uki waza) are still affecting the center line, but in a more subtle way. I'm still using my center, and I'm still attached to uke, but now shearing across his lines of movement: mae otoshi, across him to his left front corner (if he's attacked me right side), sumi otoshi to his right rear corner, and hiki otoshi takes him forward and down.
I also realized that the arm twisty thing in mae otoshi, as well as the arm lock in hiki otoshi, which both occur before the throw are get if you can get them but are really ancillary to what's really going on.
But there still, those moments, too, should affect uke's center line. The coil in mae otoshi makes uke's hips jut out a little (which makes him go up on his toes) and get his line out of whack. Uke should want to try and uncoil, to get out of that tension; when he does, then we step in and displace or shear across his center with ours. The straight arm lock in hiki otoshi should put uke on his toes, too, loading his weight back, and again, when that tension is released we shear down.
Actually, the last three I'm still working on defining and deciphering in my own mind. Perhaps another epiphany will strike someday, and they'll make even more sense.