你以为你什么都知道
[nĭ yĭ wéi nĭ shén me dōu zhī dào]
'You think you know everything.' It carries a sarcastic or critical implication as if warning others that they should not be overconfident in their knowledge or judgment. It also suggests there might be hidden or misunderstood aspects of life or others that cannot be captured by just superficial knowledge.