Image source: http://homepage.mac.com/torgo/3D%20Images/NESP/070%20Pool%20Table.jpg
When playing pool, a good set up for a shot would occur when the cue ball,
the ball you are trying to get in the pocket, and the pocket are collinear.
In this situation, a straight shot will get the ball in the pocket. Otherwise,
if the three objects are not collinear, then you have to try an angled shot.
Image source: http://www.usatoday.com/news/world/_photos/2001-06-21-zambia-eclipse.jpg
During an eclipse, the sun, moon, and earth are collinear.