What's with the script?

Question

JavaScript

There is html5 video on the background, autoplay ignores it.
I solved the issue with a js script, but there is some kind of game in general.
This is how it doesn't work:

$(document).ready(function () {
    $(".bg-video")[0].play();
});

And this is how it works:

$(document).ready(function () {
    $(document).ready(function () {
        $(".bg-video")[0].play();
    });
});

What kind of game and why is it so, because this should not be