:up: The other thing in favour of 'can' is that it emphasizes the idea of doing as much as you can..
Another idiom - similar in some ways (emphasizing the limits of what can be done) but not meaning the same - is 'You can take the <noun> out of <place> but you can't take <place> out of the <noun>' - which refers to the influence of the place you're born in on who you are: a non-PC example is 'You can take the girl out of Essex but you can't take Essex out of the girl'.
b