You don't memorize the specific details, you memorize the flow of systems. But you get back to the details to put things into practice.
So was I.
> One decompress it when they can generalize and apply it.
Generalizing is compression. Generalizing and applying are very different things.
> So understanding is compressed, but is not the act of compressing.
Understanding (noun) is compressed. Understanding (verb) is the act of creating understanding (noun) and is compression.
> The larger data it represents never existed.
The larger data is everything you take in about the subject. Experience and instruction.
What is it compressing from?