I think it means that a man (horse) have free will... you can show him the path but you can't force him to do anything he doesn't want to... Lead the horse to the water... but do you think it is going to drink without being thristy?

We use this analogy to remind ourselves that people still have their own mind and opinion, and they make their own decisions, in spite of what you explain or show them. You could be perfectly right, but that doesn't mean someone will therefore agree with you.

you cannot do everything, human abilities have limitations. hey maybe the horse isn't thirsty.