只怪年轻是人是狗没分清
[zhĭ guài nián qīng shì rén shì gŏu méi fēn qīng]
'Blame Youth, When One Cannot Tell a Person from a Dog' vividly conveys regret over misjudgment during young days. This reflects self-blame over naively mistaking someone's true nature as noble or good due to lack of experience in youth. Here, the dog might imply something that doesn't worth your respect or care.