Re: puzzled with the negative feedback system

You are hitting on the concept of "loading" and it can effect real
world circuits in ways not accounted for in situations like you
encounter in your school work. In the real world, there are ways to
avoid this issue, such as using amplifiers with high input impedance
and low output impedance to make the loading effect between the blocks
negligble. If you haven't already, you will probably implement
feedback circuits using opamps, which have these properties.

At first, however, these issues are ignored so that the student can
concentrate on grasping the concept of feedback, which can be less than
intuitive. Once these basics are undestood, then you can go back and
start to enrich the model.

.