Do we read what we share? (Answer. "No")
via Tony Haile, (emphasis mine)
A widespread assumption is that the more content is liked or shared, the more engaging it must be, the more willing people are to devote their attention to it. However, the data doesn’t back that up. We looked at 10,000 socially-shared articles and found that there is no relationship whatsoever between the amount a piece of content is shared and the amount of attention an average reader will give that content.When we combined attention and traffic to find the story that had the largest volume of total engaged time, we found that it had fewer than 100 likes and fewer than 50 tweets. Conversely, the story with the largest number of tweets got about 20% of the total engaged time that the most engaging story received.Bottom line, measuring social sharing is great for understanding social sharing, but if you’re using that to understand which content is capturing more of someone’s attention, you’re going beyond the data. Social is not the silver bullet of the Attention Web.
Or, to put it differently, humans are optimized to spread rumors, especially ones that they dont' actually pay that much attention to.