It is tricky to get someone to recognise that they aren't knowlegable enough. Even if you say it as gently as possible, some will still hear "you're dumb" and no one likes that.
Also it's a great tool to manipulate people : "I don't need a scientist trying to explain me life from the depths of their lab !! I have commonsense !!"
Guys… you can’t post this meme and not tell which one it is !