The opportunity is gone; lamenting 'shame on me' won't help.
Tips
history
From the 《后汉书·范滂传》 — the scholar Fan Pang, when wronged and powerless, repeatedly cried 'fù fù' (负负, 'I have failed, I have failed') as an admission of defeat. The reduplicated 负负 captures the rhythm of self-recrimination.
register
Highly literary; appears in op-eds and historical commentary, almost never in speech. The everyday equivalent is 无可奈何 (wúkěnàihé) or 后悔莫及 (hòuhuǐmòjí).
