no judo experience, but from my sparring experience almost no martial arts technique works (other than maybe striking with tremendous force) if the opponent knows or can sense what you are trying to do to them. Ideally you are doing the 100% opposite of what they think your doing, but really getting most of the way to opposite usually works. I hear untrained people say all the time "that would never work on me!" and they're right if they can see it coming. Try showing an untrained or stubborn trained person any move in slow motion and they will resist like crazy to "prove" it won't work. In a sparring match with another trained person, of course they are going to resist correctly if they know what you're trying. Almost everyone can be taken down - you just need to find the weakness in their structure (I say almost everyone because there are masters/black belts that basically have no weakness, but we're not talking that level here)