Electrostatic Discharge (ESD) is the sudden flow of electricity between to charged objects(i.e. your hand and that new RAM chip you just bought). Most electronic devices can be damage by ESD.
Try to think back when you would run around in your socks as a kid and the second you touch the door knob…ZAP!!! The same thing happens with electronics except that the door knob is a a cheap piece of metal compared to a complicated, expensive RAM chip. Think of it as tiny lighting that travels through the electronic component looking for the shortest path to ground. Ecmweb did a study on this and found in a recent investigation that “the human body and its clothing is capable of storing between 500V and 2,500V during the normal workday. This is far above the level that damages circuits yet below the human perception threshold”. This means you could shock and destroy your Macbook without knowing anything occurred. That is why ESD safety precautions like grounded anti-static mats and ESD wrist straps are used when working on computers or other sensitive electronics. For more info visit http://www.nfpa.org/