Blogging is primarily providing an opinion to stimulate discussion. The opinions of others are often used to support the point of view of the blogger. Sometimes, unique information for another source is added to build content.

Anytime content written by someone else is used, the source needs to be cited.

Once someone has read something, if they knowingly use either the unique way the idea was presented or the exact words, they are obligated to cite the source.

Common ideas and information, of course, don't need to be cited. But common ideas in the context of a larger body of content, expressed uniquely or quoted exactly should be cited.

After a few hours of writing the perfect post or page, it would be upsetting to see a paragraph, list or title on someone else's website. Ideas aren't always unique, but the way they are fit into context and expressed is.

Credit needs to be given for the uniqueness.