You can't convince someone they're wrong. Well, maybe you can, but it's close to impossible. The reason it's so difficult is because it requires you to speak louder and more articulate than the other person. And, the thing is, the louder you speak, the harder it is to understand what you're saying.
Instead, try a more effective approach. Help someone see a different perspective. Help them make a new decision, as it were. Provide a twist. Help them realize something they maybe haven't thought of before.
You're not saying they're wrong, you're just showing a different side to the coin. It's a new story. And, research shows, new stories perform better amongst core users over telling people their story is fiction.