Some blog owners create a post, with content that should be visible, only when required. The post contains a question - accompanied by the answer to the question. The question should be viewed, without the answer being visible, to make the reader think about the answer. This is called, by many, a "spoiler". Not everybody knows how to construct a spoiler. Some blogs use JavaScript - painful to construct, and maybe not effective for every reader. Security conscious blog readers may block scripts from Blogger blogs - and either your spoiler is visible, immediately - or never becomes visible. Neither of the latter scenarios make the post a lot of fun to read.
What Blogger won't tell you