识人识面不识心知人知面不知心
[shī rén shī miàn bù shī xīn zhī rén zhī miàn bù zhī xīn]
'One may recognize a person but cannot really know their heart' implies that appearances can be deceiving; we often do not really know a person until experiencing or communicating with them over a long period. It conveys one's feelings after being betrayed by someone they trusted before, implying distrust and wariness.