you can lead a horse to water, but you cant make him drink

You can lead a horse to water, but you cant make him drink is an idiom which means that people will only do what they have a mind to, and while you can encourage them by supporting them or leading them towards something, you cant actually force them. The phrase refers to horses and how you can lead them to water such as a creek, but you cant actually force them to drink the water, they must decide that on their own.