The opportunity is gone; lamenting 'shame on me' won't help.
Tips
history
From the 后汉书 biography of 范滂 - the scholar, when wronged and powerless, repeatedly cried 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 or 后悔莫及.
