Re: YouTube: Christian Tissier, 2014
It is good practise to allow a beginner to complete the exercise with 'some help' of tori. Getting the bigger picture, the flow of the technique is of utmost importance in that phase.
Later, when more experienced, tori will never allow himself to be off balance and takes ukemi when he feels he loses his balance. He is not thrown by aite, ever! That would indicate that he is too late with responding to the fact that he is losing (lost) his balance. In short, he just made a mistake.
We are taught that tori also does Aikido, also keeps control of the situation, does not allow himself to get unbalanced. aite/tori, student/teacher, yin/yang. One cannot exist without the other.
It is not a question of demonstration or regular practise. That suggests you do different things, which you should not. Ever watched one of the high rank 'original' Japanese teachers (Tamura, Tada, Endo, Tohei)? in demo and in lesson? no difference at all.