Re: Pain in aikido?
In a nutshell, I believe that pain-compliance is a poor substitute for kuzushi.
Practicing against martial artists that are not aikido practitioners, but are giving relaxed, focused intent, I've found it frequently that attempting to crank or force a technique through pain creates a force-on-force conflict that often gives them the time to momentarily recover and try to do something unpleasant to me (punch, kick, throw, choke . . . *gurgle*).
At the same time, when you're primary objective is kuzushi/off-balancing from your initial entry/blend, then you're less likely to be looking for an ikkyo or nikkyo and more likely to maintain your body's proper structure to achieve the off-balancing of the other person with whatever you fall into. I believe also that you train this skill through the taking of ukemi, by giving focused, relaxed attacks that have intent (not an oxymoron).
In other words, as uke, you're not off-balancing yourself in the attack, but while training the form, creating the platform for nage to off-balance you, which leads to increased sensitivity to balance and structural integrity during application drills and randori.