Humans instinctively do things everyone else around them is doing.

Spent the last half hour looking for a video I saw yesterday, but can't find it so I'll describe it quick because it's exactly what we're talking about:

There's a bunch of people sitting in a doctor's office, and the door opens. When it does everyone stands up except for an asian woman. This repeats several times, until she starts to notice and look around. Finally, she stands up too.

She wasn't indoctrinated, she observed the crowd and instinctively tried to fit in. No one taught her to stand when a door opened, but everyone around her did it so she instinctively joined in.