When you try to sell something and someone undercuts you. So you undercut him and he undercuts you again. Many people just say screw this and undercut by a huge amount.

A sells 5 Felt trouser 60k
B sells 10 Felt trouser for 59k
A undercuts by 1 k again
B undercuts again by 1k
A has enough and undercuts by 20k to scare B away.