There are many techniques in judo that are quite similar to each other. I often think that these groups of techniques that are similar are clouds or sets or technical spectra enclosed by the two most extreme forms like a set is enclosed in parentheses.
For instance, you can look at most of the ashiwaza as being somewhere between the extremes represented by deashibarai/kosotogari and okuriashibarai.
Deashi/kosoto happens when uke's center is dropping and his feet are separating. Okuri happens when uke's center is rising toward its peak and as his feet are coming together. Depending on how you set them up (straightline or round-the-corner), one happens very early in the stepping cycle and the other happens later. Much of the ashiwaza technical spectrum lies somewhere between these two extremes.
Okuriashibarai has never been my forte. I have spent 20+ years working on the beginner forms (like side-to-side nagenokata form) with moderate success, but have never been able to whip uke's feet out from under him like some of my betters. I reckon another 20 years of practice is called for. ;-)
I do, however, have a decent deashibarai and a (perhaps even dang good) kosotogari. I think this comes from having made every mistake that can be made in that technique during the past 20 years. All I have to do now, is not do any of those ;-) and deashi works great!
Want to get a good handle on most of the ashiwaza? Work on deashi and okuriashi.
Want to get a good handle on koshinage? Work on ukigoshi and something far larger and more extreme (like sodeTKgoshi)
We can probably argue endlessly about what techniques are the parentheses in tewaza - I'd maybe initially say ukiotoshi and taiotoshi. But the point is, by working on the parentheses, you get better at the stuff that they enclose.
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