This quote is so silly, and misused. It’s like one of those facts about Einstein that you’ll see on Facebook.

For one, in this context, a junior developer will rarely be the smartest person in the room. So it’s really terrible advice for the context.

I think it’s really terrible advice in general though, the places I’ve learned the most is exactly when I’m the smartest person in the room, doing stuff like mentoring or teaching.

In fact I do part time work as an external examiner at IT educations in my country, exactly because they teach me a lot. I’m almost always the smartest person in those rooms, but by evaluating i relearn/refresh things that I haven’t touched in a while.

Aside from that, you’re almost never in a room where there isn’t an opportunity to learn. Maybe you’re the best programmer in the room, maybe you’re the best architect, but you’re very rarely the best at everything, and the modern workplaces thrives the most from teams, in which everyone is the best at something, because they become more than their individual sums by cooperating.

In a non-technical environment, it is very easy for a junior developer to end up the smartest person in the room as far as tech is concerned. Think meetings with SMEs, PMs, or Sales.

The statement is if you are "the smartest person in the room", not "the smartest person in the room in one narrow area". If SMEs, PMs and Sales people aren't smarter than you in some other areas, then you are somewhere with incompetent SMEs, PMs and Sales people.

The advice is for the long haul and if you work out side of v high end RnD which you may have to do in order to get a decent salary its quite common.

Also just because your the teacher doesn't mean your smarter than all your students you may know more.