Programs are systems of interacting parts.
For a system of interacting parts to work together requires connections between these parts.
The more connections, the more costly the program.
For a fixed number of parts, a system whose parts are unnecessarily connected is more costly than a system whose parts are necessarily connected.
Unneccessary connections can only be formed in a system whose parts are unnecessarily exposed to connections from other parts.
Minimising unneccessary exposure of parts to connection from other parts is fundamental to cost-effective program development.
Loose coupling and information hiding are the fundamentals of connection-exposure minimisation.
This is not optional knowledge for a programmer.
This is fundamental.
You cannot be a cost-conscious programmer without this knowledge.
Asking how to explain loose coupling and information hiding to a new programmer is like asking how to explain surgery to a new surgeon? Or to explain architecture to a new architect? Or how to explain flying to a pilot.
If your, 'New programmers,' don't know loose coupling and information hiding, then they are not, 'New programmers;' they are potential programmers.
Curiously, it probably won't help to tell them to read the original two papers:
i)Loose coupling: 'Structured design,' by W.P. Stevens, G.J. Myers and L.L. Constantine.
ii)Information hiding: http://www.cs.umd.edu/class/spring2003/cmsc838p/Design/criteria.pdf
