senses deceived, and he unknowingly played right in to Diablo's hands.
I don't remember exactly where I saw that, but I know it was in something official.Read that somewhere before too. Definitely official, just buried somewhere within Blizzard's lore library.
Actually it says so in Diablo 1 if you pay attention to what everyone says and if you pay attention to what lazarus says in his books... Simply put he put it in his head because Diablo tricked him. Diablo actually couldn't leave the cathedral because his hosts where too weak he needed a strong host to take him out and travel east. So Diablo 1 is actually about him drawing you in to think that you defeated him and tricking you into thinking that you are strong enough to contain him inside yourself useing your body as a prison. when really (as planned) all you are doing is giving him a host strong enough. which is why at the end of diablo 1 it says you start traveling East.