From Operating System Concepts, 3rd Edition by A. Silbershatz, J.
Peterson, and P. Galvin: In the section introducing
multiprogrammming, the book makes an analogy to try to make things
clearer:

[..discussion of CPU switching from job to job instead of waiting for
I/O to finish on current job…]

This idea is quite common in other life situations. A lawyer does
not have only one client at a time. Rather, several clients may be in
the process of being served at the same time. While one case is
waiting to go to trial or to have papers typed, the lawyer can work on
another case. With enough clients, a lawyer never need be idle.
(Idle lawyers tend to become politicians, so there is a certain social
value in keeping lawyers busy.)