The Weir are a brutal, often savage race. As such, many parts of pack structure and politics are played out upon the field of challenge. Due to the fact that death is frequently a temporary state for the Weir blooded, most of these challenges are bloody, vicious, and frequent.
Position is Challenged for. Mates are Challenged for. You didn't properly show throat to someone, and that's Challenged for as well.
The most important Challenge, however, is that for the leadership of a Pack. It is this Challenge that is to the true death more often than not, the victor committing the defeated to one of the few methods of killing another Weir: Stomach, Fire, or Silver. As such, only those that truly seek power, truly believe they are the rightful leader of a Clan, will seek the position and declare their intent.