What makes you ‘Comment’ on or ‘Like’ a Post?

I have watched as I read several ‘Posts’ on these sharing avenues lately and wondered what the rationale is for readers, that is behind what they comment on and Like. So the questions are what makes readers add a comment or like a post? Was it based on the content of the post? Or was it influenced by who the author of the post is? Is it in any way influenced by personal relationships with the author of the post? Or is it a combination of these factors?