Why is it so difficult to pick a research topic?

The question that naturally comes to my mind after reading the first chapter of the Luker textbook and attempting to come up with some research questions using "ambitious and wide-ranging" thinking is: what makes it so difficult to pick a research topic? I believe exploring this question would make it easier to come up with some relevant research topics. 

For the past ten years or so, I have been a passionate reader of blogs and online discussion forums, I rarely post contributions however, probably due to the fact that, in the end I consider them to be personal opinions of the participants relating to the topics of discussion. While conducting personal online research on various topics, I often end up on blogs and discussion forums, this has me considering other potential research questions such as: How do research and blogging relate? Can objective research be somehow conducted via a blog/forum? Are participants of a blog seeking to find the truth about a particular topic? Are they rather attempting to form an opinion based on critical reviews of the different contributions? Are blogging and research ultimately motivated by the need to influence public opinion?  

Another potential topic of research I stumbled upon while considering options for purchasing/obtaining the Luker textbook (I ended up buying the e-book kindle version online from Amazon) is: Evaluating the pros and cons of printed as opposed to digital books from a reader's perspective.

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