Public speaking tip of the day: if you are talking to people, assuming they are all very smart people, and you are telling them something that goes against their common sense, then guess what: you can try to tell them once, twice, or even ten times, and you will fail to make any impact. They are not going to believe in or buy into whatever it is that you are saying.
That is, until you demonstrate what it is that you are talking about. You have to demonstrate exactly hat your concept it so they can see it, feel it, and visualize it. I could tell people all day long that they have to rehearse their speeches but they will never ever do it.
The only way I have ever been able to communicate that concept to people is that I don’t tell them to do it, I take my video camera out, have them speak, I record, I play it back, I critique, let them know their strengths and weaknesses, repeat the process again and again, and at the end of the day they notice dramatic improvement.
You are probably not a public speaking trainer so your issues are different. All I can tell you is that human beings are hard wired to not believe in something that goes against their common sense. So if you are trying to change someone’s thinking, you really have to demonstrate with a compelling example.