to know only one aspect of a thing

(offensive, Internet slang) Alternative form of 子供部屋おじさん

(offensive, Internet slang) a man whose age is greater than about thirty or forty who lives in one's child room and with one's parent(s).

single room

double room

look before you leap, one should think twice before doing something

(mahjong) a 役満 (yakuman, “limit”) hand consisting of four concealed triplets

the darkest place is under the candlestick; can't see the wood for the trees; people often known little of what happens under their noses; lit. "dark under a candlestick"