Unless I'm not understanding the terms correctly, the answer is "yes". You need to practice, train, teach your body to do new things. You need to develop a tremendous amount of skilled control. And the very process of playing involves a huge amount of focus, mental energy, intent, whatever. I was in a recital many years ago playing all three movements of Beethoven's Moonlight for a large auditorium. I remember playing about the first 2 measures of the first movement. My next memory was realizing I was letting the last note linger a bit too long. I sat back from the keyboard and realized I was drenched with sweat and vaguely started to get my orientation back. It is exhausting physically and mentally.
Thanks for the clarification, I get it now. I agree with what you are saying and I think Cady was saying the same type of thing. It just sounded like she was saying that the training process is very specific and singular (only one road leading to Rome) and at the same time extremely complex and diverse. Now, even then, it could just be one very complicated road leading to Rome. But I think Cady was talking about the thing itself in the first phrase - the This Stuff - and in the second, she was describing the training process for developing it.
It is interesting that you comment that first you figure out what Aikido is supposed to teach and then you remove the obstacles to learning that...the difficulty in figuring out what Aikido is supposed to teach is probably why we are all here in this strange little subforum in the first place. Maybe the reason why Takeda and Ueshiba got no shortage of people in the door was because Japanese folks in the late Meiji through early Showa days were starving for This Stuff. They had an notion of what the masters of yore could do and they wanted that. These days, people take up Taiji largely because they heard it was a way to keep yourself healthy as you age, and they take up Aikido because they heard it has a unique philosophy about how to resolve conflict.