Lessons must be learnt.

教训必须被吸取。

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Lessons of history must be learnt.

历史的教训一定要汲取。

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You must remember that the most important lessons in life is something like confidence, honour, love. The most important lessons just can be learnt from your experience. .

生活中最重要的东西是教育无法给予的，比如自信、幽默和爱。这些只能从你的经历和生活中得到。

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But Kenya's Standard warns against vindictiveness and says lessons must be learnt.

BBC: NEWS | Africa | Africa ponders corruption report

Senator Bob Corker, the top Republican on the Senate's foreign relations committee, said the report's findings were "appalling" and that lessons must be learnt to avoid repeating mistakes in Afghanistan.

BBC: US's $60bn Iraq rebuilding effort 'achieved little'