Horses and Clients

One of my boss' favorite lines has been coming back to haunt me often the past few days: You can take a horse to water, but you can't force it to drink. [origin]

If you have sound advice to offer, but you have the sinking feeling that the client will not be able to (or worse, will refuse to) implement it, can you still consider that advice 'sound'?

On the other hand, if we don't draw a hard line somewhere, won't all the 'tailoring' or 'customizing' we do to account for the specific circumstances of the client just be equivalent to 'watering down' our recommendations (no pun intended)?

I doubt I'll find the answers to my questions tonight. :-(