Double Edged Swords are powerful, but dangerous. They are sharp on both edges, use with caution.

Similar analogy: a double '''ended''' sword is one that has two sword ends, and allows you to stab yourself in the hand. Hold the sword in the middle and avoid stabbing your hand. But you can still stab your stomach accidentally, even if you hold the sword in the middle.

http://s3.hubimg.com/u/1110690_f496.jpg 

Pointers in Cee: double edged sword, shoot or stab yourself in the foot. Yet powerful, pointers are. 

Google: double edged sword; can be misused to find information that is fallacious, yet it is one of the powerful ThinkingTools.
* Example: religious nut finds this: http://www.theflatearthsociety.org/wiki/index.php?title=FAQ  ...the earth is FLAT, not round!