I’m not into it either, and I’ve never heard that. Could the humans have avoided some of the grim darkness if they had good advice?
i have some surface level knowledge,
and i also cant recall anything like that.
id say that the majority of humanitys issues are self inflicted.
it is unlikely that eldar would disclose such an issue,
but its just as unlikely for humans to follow such advice.
informing the humans would probably just result in them raiding said tombs actively worsening the situation.
To be fair, the Eldar tried to warn the emperor, but the Primarch they found had already fallen to chaos. Fulcrum, if I remember right.
About the horus heresy. Sorry, I implied that, since that’s the big turning point, but I should have made it explicit.
About the Horus Heresy
