Writers are always advised to write about what you know (which can be difficult for authors of sci-fi, horror and fantasy in particular when you stop and think about it! We are inventing new worlds. How can we possibly "know" something that does not exist except on our pages? I suppose the what we know here is knowing in good enough detail the world we've created and inventing characters readers can identify with. Knowledge of human nature is crucial here).
But there is reality in fairytales. Not just of character types. Whatever world you write about, characteristics do not change much. There will always be those who lust for power, the oppressed, those who fight back, those who go on seemingly impossible quests because they have to save something/someone and this is the only way to do it and so on. (Great stories come from the last category alone, think The Lord of the Rings to name but one).
When I think of a realistic fairytale, my mind nearly always turns to Hans Christen Andersen's The Little Match Girl. Definitely not one of his cheerier tales but, without giving too much away, to be able to write this as well as he did, he had to know something of poverty (which he did) and I strongly suspect he actually saw real match girls which inspired this tale. To me this story is a barely disguised report on something he saw and his underlying jibe at people being allowed to suffer like this girl did is as hardhitting now as it would have been when he first wrote the tale.
Often with fairytales it is the message behind them that is the realistic bit. I think this is why fairytales have always resonated with people and always will.