Did you know (DYK) is where facts from new articles or those newly promoted to good article (commonly referred to as GA) appear on the main page.
Examples of bad hooks include those that (almost) everyone knows. These are also not interesting. Also note that these are only my examples, not real life DYKs.
Ones that (almost) everyone knows
editLanguage
edit'there are 26 letters in the English alphabet?' could be replaced by 'that there are only 21 letters in the Italian alphabet?' because it shows that Italian doesn't use the five letters that English uses, at least in native words. Other examples include 'that almost every Italian word ends in a vowel?'
Mathematics
edit'division is the opposite of multiplication?' could be replaced by 'that it is not possible to divide by zero?'