> There is an incredibly strong “birds of a feather flock together,” effect at play

Agreed.

As an engineer who doesn't take any stimulants, what does it look like when another person is on Adderall? Maybe I'd notice a person snorting cocaine at work, but if I saw someone taking a pill? I'd figure it's probably just a painkiller, or a multi-vitamin, or for some health condition. Never would I suspect Adderall or some other stimulant. I basically presume that nobody at my office takes Adderall because I would never take it myself.