Why Is the Process by Which Prospective Buyers "Internalize" or Consider

Why is the process by which prospective buyers "internalize" or consider the information presented by the salesperson referred to as a black box?

A) for every action there is a reaction
B) we cannot see into the buyer's mind
C) it's like a black hole in space-things go in, and are never heard from again
D) for every stimulus, there must be a response
E) there is a tendency on the part of prospects to not trust what they are told by salespeople