From the same source (highlighting mine):<p>Human needs arrange themselves in hierarchies of pre-potency. That is to say, <i>the appearance of one need</i> usually <i>rests on the prior satisfaction of another, more pre-potent need</i>. Man is a perpetually wanting animal. Also no need or drive can be treated as if it were isolated or discrete; every drive is related to the state of satisfaction or dissatisfaction of other drives.