You can take a horse to water but you cannot make him drink

Origin
This metaphoric term dates from the 12th-century and was in John Heywood’s proverb collection of 1546. It first appeared in the Old English Homilies in 1175.
Explanation
It is used for emphasizing that you can make it easy for someone to do something, but you cannot force him to do it. In general usage, the meaning is usually thought to be, “You can show people the way to do things, but you can’t force them to act,” or, “You can give someone the opportunity to learn or to do something, but you can never force him to accept that opportunity,” or, “You can offer something to someone, like good advice, but you cannot make him take it,” or, “You can help someone as much as you like, but if he does not try or does not help himself, then he will not succeed.” 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.
Example
Jill: I told Katy about all the jobs that are available at our company, but she hasn’t applied for any of them. Jane: You can lead a horse to water, but you can’t make it drink.