This is a great read. Hopkins practically founded modern advertising. He advocated for measuring everything and testing everything and holding advertisers accountable for results in 1927. Before the internet, before big data, before conversion tracking.
David Ogilvy said: "Nobody should be allowed to have anything to do with advertising until he has read this book seven times. It changed the course of my life."
It's required reading for anyone that uses words to convince other people to do things.