Jane

In my first weeks at the dojo, I'd get to work with a sempai who's always so contracted: he hardens his body all the time. When I'd be supposed to move forward, he'd be pushing me away, saying something like I should "force the technique in".
I was really frustrated. My sensei told me that when a partner did that, I shoud change the technique to take him off-guard.
What I've learned from these experiences is that a good uke shouldn't try to humiliate his partner by preventing him from studying the technique, nor be too obedient: I've been kicked by sensei's wife for "falling without obligation"!
Aikido is about ki flow, not brute force so, at least during pratice, none should have to use strenght to complete the techniques.
And as for, what's the yudansha's technique's worth on the street, there are some things to remember: the attaquant won't know what nage is about to do and unless nage makes a mistake, well, he should be able to handle the situation.
ciao!