Idiom Definitions for 'Walk a fine line'
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If you have to walk a fine line, you have to be very careful not to annoy or anger people or groups that are competing. ('Walk a thin line' is an alternative.)
1. There's a fine line between boastful and confident. And you need to learn it.
在自负和自信之间有一条线，你需要知道这条线在哪。
2. Others say that there's a fine line between the pageants and sexual exploitation.
其他人说，选美和性剥削之间只有非常细微的界线。
3. She wished he would stop talking like that, but Minmei knew she was walking a fine line again.
她希望他不要再那么说话，可明美知道自己要小心行事才行。
4. Luxury-goods executives must walk a fine line when cutting prices.
奢侈品行业人士降价时必须特别谨慎。
5. So, you know, when I'm playing well on clay, it's a fine line that I kind of have to walk between those two.
所以你知道，当我在红土上打得很好，那么我需要掌握好这两方面。
It means to steer a risky and difficult course between two policies... to be so near the edge of one that you risk falling into another less desirable one. All of which is a pretty unclear definition, so maybe an example might help.
（下面这个句子和你的问题很相似）
"With his current policy approach towards Iraq, President Bush walks a fine line between the interests of national security and those of warmongering."
The metaphor's from tightrope walking, I'd guess.
朗文和麦克米兰和柯林斯词典都没有walk a fine line的解释这是一个新词语，应该是由walk a tightrope （这个idiom是可以在朗文上查到的）而来，国外论坛上也有人这么猜。
A fine line is a very thin thread like a fishing line.
正好我也看着CNN里面提到了a fine line to walk..一起学习吧。