Why isolate “lower” application layers from “higher” layers?

Why isolate “lower” application layers from “higher” layers?

Feb 1st 2014, 17:45, by Stack Exchange

Stack Exchange

This Q&A is part of a weekly series of posts highlighting common questions encountered by technophiles and answered by users at Stack Exchange, a free, community-powered network of 100+ Q&A sites.
Jason Swett asks:
In a typical (well-designed) MVC Web app, the database is not aware of the model code, the model code is not aware of the controller code, and the controller code is not aware of the view code. (I imagine you could even start as far down as the hardware, or perhaps even further, and the pattern might be the same.)