Isn't it strange?

I just realized, the Einherjar's actually only disappear when no one is left to remember them, the ones who are left accept that they're dead, or the fighter fully gives up, take Adam for example, he took the longest to actually disappear, why? humanity believed in him, until Heimdall said that Adam died, we slowly accepted it, and next one is Lu Bu, the way he disappeared is much more confusing, because only after his entire army is dead, he started to disappear, because everyone who was in the stands accepted he was dead, and his army held him close to their hearts more than everyone, then there's Raiden, he just gave up