防人之心不可无毕竟世上狗太多
[fáng rén zhī xīn bù kĕ wú bì jìng shì shàng gŏu tài duō]
It means one should be cautious of others, as there are too many deceitful people in the world. Here, 'dog' metaphorically represents untrustworthy or deceitful persons, reflecting a kind of negative social attitude or experience.