Small Gods (Discworld, #13)

by Terry Pratchett

A handful, though, go on to greater things. Anything may trigger it. A shepherd, seeking a lost lamb, finds it among the briars and takes a minute or two to build a small cairn of stones in general thanks to whatever spirits might be around the place. Or a peculiarly shaped tree becomes associated with a cure for disease. Or someone carves a spiral on an isolated stone. Because what gods need is belief, and what humans want is gods. Often it stops there. But sometimes it goes further. More rocks are added, more stones are raised, a temple is built on the site where the tree once stood. The god grows in strength, the belief of its worshipers raising it upwards like a thousand tons of rocket fuel. For a very few, the sky’s the limit. And, sometimes, not even that.