For viral videos, I would say a lot of luck for sure.....and usually, they're something odd, intriguing, quirky......I mean..look at 'sittin' on the toilet'........just some random video of her singing that, gets millions and millions of views.....people want to share that because they want to talk about it, like "have you seen this crazy video?" etc. As for Vlogs going viral, it takes luck, but also, a lot of personality and hard work too
No doubt about that!