Stories gain weight as they travel, not uniform infection rates.
Virality is something which is equally infectious at each stage. If I have a story which one out of 10 people like, that story doesn’t change. One out of 10 people like it in the future as well. Contagiousness is different. As long as it travels, it gains weight. The more people believe in it, the more trustworthy the story becomes. Even a wrong information becomes more believed the longer it travels. At some point everyone believes it’s truth no matter what because so many people believed in it. Forget about virality. The right word is contagiousness.
— Measuring Social Media What Marketers Need To Know · Social Media Examiner