Much has been written over the years from a parenting point of view about the so-called "generation gap." Anyone who is now, or has EVER grappled with the responsibility of raising a teenager is qualified to write a book on the subject, and from the number of them on bookstore shelves, probably HAS. The generation gap also raises it's troubled head in art as well. The Mannerists were just one generation removed from the Renaissance. The same was the case with the Post-Impressionists. Each generation of artists is raised by the PREVIOUS generation, and perhaps because of that there develops a love-hate relationship that is sure to penetrate the art of the second generation. The Post-Impressionists grew up with Impressionism, were not shocked by it as had been their grandparents, but neither were they awed by it. They recognized it's beauty and appreciated the hard-won freedom of creative expression the Impressionist generation had wrestled from Academic tyranny.
But Paul Gauguin, Vincent Van Gogh, Toulouse Lautrec, Paul Cezanne and all the others also recognized the weaknesses this art movement had encumbered within it. They rebelled against it's slavish devotion to the outdoors, to its wishy-washy drawing, it's subservience to the visual world, to it's observed color theories, and most of all to the overwhelming dominance of the LANDSCAPE as the lord god almighty of subject matter. In some cases it was rebellion for the sake of rebellion as in the painting of Paul Gauguin. It other cases, such as Van Gogh, it was a search for more emotional relevance as opposed to the intellectualism of Monet or Manet. Sometimes it was an attempt to legitimize Impressionism and stabilize it as in the case of Cezanne. In other cases, the emphasis seems to have been or producing a sort of "super" Impressionism as with Lautrec.
So in other words, what we see happening in the aftermath of Impressionism is a robust diversionism, everyone going off in their own direction with only a very general artistic relationship to each others work or that of their Impressionist forebears. They had little in common stylistically (unlike the Impressionists), but were linked only by the thin, common thread of unfettered creative exploration of everything that was NOT Impressionism and a devotion to that which was "modern." If you give an artist TOTAL freedom of expression you do so at great risk. He might decide to paint the inside of a brothel or the OUTSIDE a nondescript town hall. He might decide to paint the OUTSIDE of himself by depicting what's INSIDE him. There was rebellion to be sure, but most of all there was exploration--a breaking down of subject matter and stylistic barriers even the upstart Impressionist hadn't dared touch.