'You cannot reason people out of an opinion they have not reasoned themselves into.'
That's a modern way of saying what Jonathon Swift observed in 1721.
Wouldn't persuasion be so much easier if we humans were entirely logical? The research makes it clear that we're not. We just think we are.
We treat our own opinions as more logical and well-informed than other people's opinions. We may not go as far as talking about alternative facts and rejecting other people's information or opinions as fake news, but it's only human to struggle with objectivity.
How much of a struggle?
Psychologists have studied more than 90 ways we humans compromise our objectivity. Let's just look at a selection.
Are you thinking that facts will always win an argument?
Facts and data have limited power to persuade. Present us with facts and we'll start filtering. We'll quickly accept facts that support our view of the world and forget or reject facts that don't. We'll even be working on counter-arguments while you are talking.
Intelligent people wouldn't do that? Intelligent people are more likely to come up with creative counter-arguments.
Find common ground. Present your argument in ways that show we are aiming for the same goal.
The classic case is persuading parents to immunise their kids. 'Immunisation is safe' and 'Immunisation doesn't make kids autistic' won't work as well as, 'Here's a way to ensure our kids are safe from the big diseases'.
Want to persuade your executive team to spend money on a more expensive machine than the Kamakuza model they think will keep their costs down? Focus on 'return on investment' - things like efficiency, reliability (so keeping production uninterrupted) and lower maintenance costs.