The gap between the public's awarness about different tragic events -and the number of casualties of the event
Comparison between 2 tragic events- Sabra and Shatila and 9/11- which nearly caused the same amount of deaths. However, the way both of them are coverd by the media is totally different.
The muslims are usually expected to apologize for "terrorist attacks" done by other muslims. However no other religious or political group is expected to offer any kind of apology for the terrorist attacks which are ironically mostly done by none muslims during the world history.