there is a huge difference between understanding what something is and actually working with it / being proficient with it. huge.

I understand how a car engine work. I would actually explain it to someone that does not know what is under the hood. Does that make me a car mechanic? Hell no. If my car breaks down I go to the dealership and have them fix it for me.

My car/car engine is ASM/OS Internals/writing a compiler/etc.