It takes time to persuade men to do even what is for their own good.

Being right is not the same as being persuasive, and few people change course on the strength of an argument alone. Even a change that would plainly help them asks them to admit the old way was costing something. That admission takes far longer than the reasoning does. Impatience at this point usually reads as contempt and hardens the very position you were trying to move.

If you have been repeating yourself to someone, lower the frequency and lengthen the horizon. Say it once, well, then let it sit. People often come round in private, on their own schedule, and need room to do it without losing face.