It's one thing to say "I don't understand it, that's why I'm staying away from it", it's another thing to say "I do understand it, you should stay away from it

It's one thing to say "I don't understand it, that's why I'm staying away from it", it's another thing to say "I do understand it, you should stay away from it and here's why", but I'm not sure why anyone would listen to somebody who says "I don't understand it but you should stay away from it."