Question: In Tamil, there is a proverb that translates to something like this:

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> A tiger will not eat grass, no matter how hungry it is.
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It essentially is used to describe a situation in which no matter how dire of a situation you're in, you will not use your last resort. In this case, it's used to describe that even if a tiger is starving to death, it won't eat grass (because it's a carnivore). I really couldn't find any sort of English idiom that can accurately describe this Tamil proverb. **Please post all related English idioms as answers, even if they are only partially accurate.**

A possible situation I might use this in: Alice was a hardworking student who believed that she could receive an A in her class without using extra credit. 

I might use the idiom to describe Alice in this situation, as she refuses to use her last resort (extra credit), no matter desperate she is (because she believes she can earn an A without extra credit.)

Answer: 
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> [You can take a horse to water but you can't make it drink](http://idioms.thefreedictionary.com/You+can+lead+a+horse+to+water)
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is an idiom that means that you can present to people a favorable situation for which all they have to do is act to take advantage of, but you can't force them to do this good thing for themselves. This is sort of like advice, you can give it but you can't make someone take your advice.
***bred in the bone***, from [Dictionary.com](http://www.dictionary.com/browse/bred-in-the-bone)

> 
> 1. firmly instilled or established as if by heredity
> 2. deeply committed or resolved; unwavering
> 
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> the proverb “What is bred in the bone will not come out of the flesh,”
>  first recorded in England (in Latin) circa 1290, widespread in various
>  versions since the 15th cent
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From [Oxford Reference](http://www.oxfordreference.com/view/10.1093/oi/authority.20110803095525826)

> 
> Lifelong habits or inherited characteristics cannot be concealed ....
>  .. in earlier usage often contained a negative (as in John Heywood's Dialogue of Proverbs (1546), ‘It will not out of the fleshe, that's bred in the bone’
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