The answer to this is complex. Big brands not only utilize funny or "meaningful" video and advertising to create a personal brand, but they use the big bucks to plaster this concept over all four corners of the Web Universe. They attempt to create either meaningful branding that people will remember or a personable presence in cyberspace and the real world.
Without access to the 'big bucks', how do regular web citizens go viral?
It's simple! For every share on Facebook, for example, you are likely to get between 10 and 100 views- depending on the popularity of the sharer. There are simple metrics that determine whether you will "go viral". If, when viewers see the post, video, photo or other item, they determine it is worth sharing, you will see your number of overall viewers jump proportionally. Enough shares (and enough steady sharing from that point) and the item in question will pick up steam.
Essentially, the answer is that to go viral, you have to create content which *is* in fact viral. Viewers will share what they wish to.
Big brands are capable of going 'viral' in a numeric fashion simply by boosting advertising and pouring money into metrics. However, there is a difference between worthwhile content that simply needed a little boost to go automatically viral, and content so lackluster that a big name brand spent several thousand promoting it.