学到的第一课是，教训是可以吸取的。

The first lesson learned is that lessons can be learned.

youdao

有些企业在一段时间内成为了时代的宠儿，又据此对未来做出了过于乐观的预期，哈雷的经验教训正好为这些企业上了一课。

There is a lesson here for companies that become the flavor of the moment -- and then use that as a base from which to make forecasts for the future.

youdao

从我们的教训中学到的第一课是，单纯使用武力无法取得积极的效果。

The first lesson that can be drawn from our experience is that the use of force alone gives no positive results.

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