What does, you can bring a horse to water but cant make it drink mean?

The way that I've always interpreted this is that you can show someone an opportunity but it's up to them if they choose to accept it. It's basically about making personal choices rather than being forced into something.

It means that you can give someone everything they need to succeed, but in the end, you cannot force them to succeed, such as a grat education, or a great job, or career path. it is one of the little twists in life.

More or less, it means you can tell someone something, or give them proof of sometihng but its up to them to apply it or believe it. Just like you can take a horse out to drink water but its the horses choice, if he will. So essentially its the choice of the person to believe something said. Hope this helps