Along with what Monte said, Roland (in the poem) rejects the macabre landscape leading to the tower bc of its grotesqueness. This rejection of the outer, leads Roland to introspection and he remembers a betrayal by one of his fellow knights. It doesn't go into detail, but the experience is so jarring that it forces Roland to open his eyes and continue his quest- he can't bare the thought of his memories concerning the event. I definitely think this was in King's mind, but when it is finally recalled it was extremely anticlimactic for me.