An example. Say I have a character named Joe. He's tracking someone. He gets out of his jeep, crouches down in the middle of a dirt road, and maybe fingers some dirt. My sentence: “Joe scanned the horizon. They were getting away, and he was completely powerless to do anything about it.” There’s no doubt here who’s doing the thinking.
This is a technique we've all no doubt read in novels before (and now that I'm further along in my writing I employ it without thinking), but when the article spelled it out for me those many years ago, I remember having a Eureka moment.