Every human act is a response to a personal need. The motivation for all personal behaviour is to produce a sense of "feel good", a sense of inner peace and well being. To expect a person to go against his desire to feel good or as good as he can feel under any momentary condition is illogical and irrational.
That a user should not be kept waiting unnecessarily is an obvious and humane design principle. It is also humane not to hurry a user; the more general principle is: Users should set the pace of an interaction.