know (one's) place
To be aware of the limit of one's role in a particular place or situation. I know my place, so I don't bother the CEO when I see him around the office. I'm just an intern, after all.
know one's place
Behave suitably for one's position, rank, or status. This idiom often has the sense of "to behave humbly, not criticize ones' superiors," as in Sorry, I know my place and I can't tell you more about my supervisor's plans. [Late 1500s] Also see put one in one's place.