Here's the best way to get a video to go "viral": Employ a large marketing firm and spend several hundred thousand dollars getting publicists to send it to places like "Ellen" and "The View" and the local news. What? Does that sound wrong? Well, sadly, that's how most "viral" videos are made. They're created by brands and if you look closely, you'll see branded merchandise in the backgrounds or foregrounds of a lot of "viral" (or "virally marketed') content. It's sad, but that's the landscape of YouTube nowadays. It's mostly meant for brands pushing products.
I was very pleased to see the "Chewbacca Mom" wasn't a marketing ploy by Kohl's, but then they took that opportunity and ran with it, so I suspect a lot of that push after she got a ton of views (Facebook views, so not monetized, most likely) were done by them.
There are some truly "viral" videos that still get out, but they're really rare, and it's almost impossible to predict when that'll happen. You can't try to make viral content, you just have to capture something amazing or strange in the moment. That's why I say to carry your camera or have your phone at the ready to capture anything that has some wow factor around you. It's going to be the thing that you don't plan at all that may go viral, rather than that perfectly-crafted moment you've spent a lot of time on.