知人知面不知心知面知心不知人
[zhī rén zhī miàn bù zhī xīn zhī miàn zhī xīn bù zhī rén]
This expresses the concept that knowing someone superficially ('face') is not the same as truly understanding their inner thoughts ('heart'). Similarly, it implies that just because one understands another's heart does not mean one really knows them fully, reflecting on human complexity.