Don't both 關心 and 在意 mean the same thing? I recently learned a sentence: 大家都和關心也很在意這件事
However, don't both 關心 and 在意 mean the same thing -- to care about? Is there a difference?
It should be &quot;大家都很關心也很在意這件事&quot;
When two different words have a shared definition, they can be used interchangeably in some context. See my answer to this question:  Are there any two chinese words which can be used interchangeably?

關 = relate; 心 = heart


關心 : to be concerned; to worry about; care about

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在 = in/at/on; 意 = mind


在意 : take notice of; care about; take to heart

If they can be used interchangeably, then you can also use them concurrently, to make them reinforce each other as synonyms
Example:
&quot;大家都很關心也很在意這件事&quot; &quot;Everyone cares about and take notice of this&quot;
The subtle difference:

關心子女安危 (concern about the safety of one's children) expresses a more serious manner than  在意子女安危 (care about the safety one's of children)

我不在意浣熊在我後園出沒。 (I don't care about raccoons coming and going in my backyard.) expresses a more casual manner than 我不關心浣熊在我後園出沒。 (I am not concerned about raccoons coming and going in my backyard.)