/lit/ - Literature

Marcel Duchamp claims that reading Max Stirner's 'The Ego and Its Own' was a major turning point for him. Before then he had been making some visually interesting cubist/futurist works that for their time were quite controversial. After that book is when he started with Dada and the toilet readymade was introduced.

I personally see this as perhaps the first point of decline in art, possibly something we've never recovered from and have gradually slipped lower and lower since.