不是所有人都口是心非
[bù shì suŏ yŏu rén dōu kŏu shì xīn fēi]
'Not all people have hypocritical nature'. It speaks volumes on human authenticity versus pretentiousness. The author might intend highlight belief that honesty still resides within certain people despite prevalent insincerity found around, suggesting some are true to their heart's content.