it happens when competition results in  mutually-detrimental outcome.

ex .     one small market that can sustain only one firm  with the playoff matrix as below 

                out          In

    In       (100,0)     (-50,-50)

   out    (-50,-50)     (0, 100)

[此贴子已经被作者于2009-2-9 19:56:23编辑过]