When did you truly learn what "reading the room" means?

"Read the room" is one of those pieces of advice we hear all the time, but nobody really explains what it looks like in practice.

One example that always comes to mind is The Devil Wears Prada. When Andy first joins the magazine, she walks into meetings treating them like any other workplace. She isn't lacking intelligence or capability, she simply hasn't picked up on the unspoken expectations and dynamics around her.

I've seen similar moments in real life. Someone walks into a meeting with a well-prepared presentation, only to lose the audience within minutes. Nothing they say is technically wrong, but it's obvious to everyone else that the timing or approach just doesn't fit the mood of the room, it just feels off.

When did you truly learn what "reading the room" means? What experience or lesson has stayed with you?