One way to always be believed is to always say reasonable, believable things. Things that other people already mostly believe or at least want to, whether it’s about you, the world, or themselves. If you limit yourself to always staying neatly within the lines of “believability” in this way, then likely most people will nod their heads in agreement when you speak.
Of course, you’re likely not saying anything that’s true, relevant, interesting, or important if that’s the case.
People like to think they’ve got it all right. That their world view and collection of facts, even if incomplete, isn’t incorrect. Sure, there might be things I don’t know, but those things all would fit neatly with what I do know if I learned them.
But a fact that not-so-gently nudges one of my existing thoughts out of place, never to find a comfortable resting place again? Well, that’s just unbelievable.
So don’t take it personally. People are people. You could spend a lot of time fruitlessly trying to convince them – or you could spend much more productive time acting on the things that are true in your own life.