If not the greatest, YouTube is certainly the biggest video site out there. There's content on it to keep you and your family entertained for generations without having to watch anything twice.
But that doesn't mean that you won't get into situations where you can't watch something that's readily available on YouTube, just not to you.
Be it because of copyright issues, terms of use violations, or rights owners being picky about who and where can watch their videos, there's plenty of content that's not available, like the video above.
Stumbling onto a video but then not being able to watch it is not the greatest of user experiences, which is why YouTube makes it possible for developers to screen out video that users of their apps or websites won't be able to view.
There are several ways of doing this, YouTube has a list of all the possible scenarios in one informative
post.