A blockquote failure (or blockquote fail) is the inevitable outcome of a messed up blockquote tag. It's a common occurrence in Pharyngula threads and the source of much frustration.
Blockquote failures can take many forms, from missing blockquotes to the whole comment ending up inside one. Unintentional nested blockquotes are also frequent, and there have been cases of entire blocks of text being eaten by a rebellious blockquote tag.
Because of a quirk in ScienceBlogs' software, if one puts more than one paragraph or even two or more lines separated by a hard return in a blockquote, only the first paragraph or line will be in the blockquote. The fix for this is to put <br> after each hard return.
Typos and unclosed tags are among the most common causes of blockquote failure. Needless to say, this is a case where preview is your friend.