There's always someone more invested. Management can pay lip service to flat hierarchies and all that, but at the end of the day structure emerges more or less by consensus, the same way everybody realizes the guy who always farts or something. The common-if-not-genetic "desire to be led" causes people to produce hierarchies for themselves, to produce their leaders. This isn't robotic, but it comes naturally to a lot of people, even if only to confer authority upon that person.