One of my favorite Chinese sayings is: 大智若愚 (da4 zhi4 ruo4 yu2), which basically means "very wise people appear to be fools." I like it because sometimes I do dumb things, and then I can say that to myself to feel better.
It is actually part of a larger saying: 大勇若怯，大智若愚 (da4 yong3 ruo4 qie4, da4 zhi4 ruo4 yu2) "A great hero may appear timid, the wise may appear foolish." So it is saying that people with great talent or great characteristics are often not recognized for what they are.
It also means that a truly wise or brave person does not go around saying how brave or wise they are. A wise person knows that, as Confucius said:
三人行，必有我师焉。(san3 ren2 xing2, bi4 you3 wo3 shi1 yan1)
择其善者而从之, (ze2 qi2 shan4 zhe3 er3 cong2 zhi1)
其不善者而改之。(qi2 bu4 shan4 zhe3 er3 gai3 zhi1)
"Of any three people I walk with, one will be my teacher.
I can learn from their good characteristics,
And I can change myself by noticing their faults."
(Or as we liked to joke in grad school: 三人喝，必有我醉。(san3 ren2 he1, bi4 you3 wo3 zui4). "Of any three people I drink with, I will definitely get drunk.")
The point being that you can learn from eveyone you meet in some way or another, so it does not pay to pretend you know everything. Hence, you may appear to be dumb if you are actually listening to say, the Information Technology person at work talk about opening and closing Microsoft Word, BUT she might say something you don't know such as "The longest recorded flight of a chicken is 13 seconds," which you would not catch if you just said "I know" and left the meeting.
Another word besides "愚 yu4" for "dumb," or "idiot" include this one, which caused me some grief at first, but now I embrace it: 笨 (ben4). Yep, my first name in Chinese means dummy. But, that's OK. As a kid I called myself Benjy, which would equate to 笨妓, ben4 ji4, or "dumb prostitute." Naughty cross-translations are always good for a laugh at parties. And if the truly wise appear as fools, then surely those who appear (via their name) as "dumb prostitutes" are practically omniscient, no?