What do polyglots mean by "This language is not for beginners"?

I really don't get it. Why is German considered "hard" while French is not? Portuguese is a "easier" Romance language than French and Spanish? What makes Korean "easier" than Japanese and Chinese? I've seen so many conflicting opinions from polyglots, and I'm a complete beginner, so you all know better than me!<br><br>Edit: I want to know why polyglots say it, not what beginners think about the difficulty of language. Example: I personally think German is way easier to pronounce than French, and so much better grammatically, but polyglots usually think the opposite!