On a Mac without an eject key (like the MacBook Air or MacBook Pro Retina Display), you can force your computer to shutdown at any point by pushing
Command + Control + Option + Power button.
or
Control at the same time as the Power button (or Eject + Power button if you have an Eject key)
Before you resort to this, first try a force quit on a problem application by pushing
Command + Option + Esc.
