"Facebook and Instagram… ask you to interact with other users in a strictly subordinate way, in comments or likes, below a post. Twitter and Tumblr are more aspirational: You can reshare other users’ posts as your own, and other users can reshare yours, with your name clearly attached.
Think of it this way: On Instagram, it’s nearly impossible to go viral. On Facebook, content constantly goes viral. On Vine and Twitter, people go viral. Retweets are rewarded with follows, and follows are rewarded with more retweets. It’s not a true meritocracy but it can, under the right circumstances, feel like one."