In the past, what pain have I linked to doing it?

我把作这件事和过去什么痛苦联系在一起了？

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The other day I went to a presentation of six high tech startups and not one of them had a clear idea for what pain they were proposing to solve.

有天我去看六个高科技创业公司的展示，没有一家能说得清他们解决了啥问题。

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And if you don't believe me, ask a child what it's like to grow up with an unhappy parent, or ask parents what pain they suffer if they have an unhappy child.

如果你不相信我，问问小孩和一个不快乐的家长一起长大是什么感觉，或者问问家长如果他们有一个不快乐的小孩，他们会承受什么样的痛苦。

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"One thing I've learned over life is that you don't really know what pain is or joy is until you experience the other."

VOA: standard.2010.03.25

Yet somehow it was transformed into, what it's turned into, a beautiful thing, although not without pain. -Yes.

但您的一生却，得以转化成另外一种美，尽管伴随着苦痛，-是的。

普林斯顿公开课 - 人性课程节选

I won't get into definitions of what torture is but it would cause somebody tremendous pain and anguish to keep them from sleeping.

我就不解释什么是施刑了,如果不让人睡觉的话,会给人造成巨大的痛苦。

耶鲁公开课 - 心理学导论课程节选

What pain, what boredom, what insecurity has led them here?

FORBES: Seattle 'Superhero' Phoenix Jones Arrested on Assault Charges

Burns places automotive foresight at the intellectual crossroads between what the majority of consumers really want (or what pain they want to avoid) and what pundits and ideologues think would be a better solution.

FORBES: Nonsense futures of the automobile straightened out by some basic consumer cost-benefit thinking

So my best answer for your first question is that yes, ketamine might help your pain, depending on what type of pain problem you've got.

CNN: Is it safe to use ketamine as a pain drug?