I don't really know any catchy 'Zen' sayings. If my training partner asks me "What am I doing wrong?", and keeps repeating the question, then I'd have to answer them directly to the best of my ability. ( If I actually _know_ what they are doing wrong), I'll tell them in as few words as possible. If I don't, then my first response still stands. Sometimes a short, one word 'tip' will steer someone in the right direction. Usually, though, I need just as much help as my partner.
Another aspect to consider is that often times uke takes ahold of nage's forearm and just stands there, waiting for nage to perform the technique. Movement on the part of uke really helps nage learn the technique. "What am I doing wrong?" can often be solved by what uke 'isn't doing right'.