You can lead/take a horse to water, but you can’t make it drink
Definition 1 of 1
Pro Tip 1/3Usage Context
Best used in informal discussions to express frustration or acceptance of a person's free will. 
We provided training to all employees, but you can lead a horse to water, but you can’t make it drink.
Pro Tip 2/3Not Literal
It's a metaphor. Don't use it to describe actual horse behavior or literal water. 
Her tutor explained the math concepts thoroughly, yet you can lead a horse to water, but you can’t make it drink.
Pro Tip 3/3Avoid Judgement
Use it to state a fact, not to criticize someone for not taking an opportunity. 
He didn't use his gym membership, but you can lead a horse to water, you know?