You can lead a horse to water, but you can't make it drink
It means that you can give someone all the opportunities needed to learn or do something, but it will be in vain if the person concerned doesn’t want to do it.
‘Brewer’s Dictionary of Phrase and Fable’ attributes it to Heywood in 1546. There is an account of an earlier origin here.
As an aside, Dorothy Parker was once asked to make a pun of horticulture, and came up with,
'You can lead a whore to culture, but you can’t make her think.'