Before such a change will occur, however, the essential cause of one's self-loathing needs to be apprehended.

然而在改变发生之前，我们需要先领会自我厌恶的本质原因，我不是指历史原因。

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Most of these micro-organisms cause no problem, and many, like the ones that normally live in the digestive tract and produce life-sustaining nutrients, are essential to good health.

大多数这些微生物不会引起任何问题，而且许多微生物，像那些通常寄生在消化道并产生维持生命的养分的微生物，对良好的健康是必不可少的。

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The mind has another essential attribute: an overdeveloped sense of cause and effect which primes us to see purpose and design everywhere, even where there is none.

我们的心智还有另外一个基本属性：一种过于发达的因果观念，使得我们时时处处都要找出事物的目的与意图，即使有时实际并不存在。

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The boards say they are distressed over the potential harm an outdated or unsuitable contact lens can cause, making verification of a valid prescription essential.

FORBES: An Eye For An Eye

"If travel is essential, the public should avoid exposed or coastal areas where gusts could cause significant harm to individuals, " he said.

BBC: Wind damaged house

On the face of it, genes that cause diseases do share one thing: they are, in a technical sense, non-essential.

ECONOMIST: Genetic disease and evolution