旧情复燃的后果是重蹈覆辙
[jiù qíng fù rán de hòu guŏ shì zhòng dăo fù zhé]
'The Consequence of Rekindling Old Affections is to Repeat Past Mistakes.' This implies a sad realization about repeating unsuccessful past relationships, warning against going back to a problematic situation that did not work before.