Most electrical devices manufactured today are double insulated.  Without getting crazy technical, that means that the appliance is designed to better protect the user from an electrical shock. Plugs are polarized to add to the overall electrical protection.  This is all good. Now I know you are waiting for the “but”, so here we go. But, we do not always use our electrical devices and tools in places that are deemed safe. How many times have we operated 120 volt devices in wet cellars, outside, or on cement garage floors?  Those situations challenge the insulation integrality of any 120 volt device. Electricity wants to go to ground or earth. That is a fact of physics and the way electricity is distributed to the grid we draw our power from. Electrical current has no issue going through our bodies in its effort to seek ground.  In my younger and more foolish days, I have had occasion to have current go through my body on its path to ground. It is incredibly painful not to mention very dangerous. So do we stop using our electrical devices in less than ideal locations? Give up a tool? Never. Ground fault circuit interrupters were invented (GFCI).  This breaker or outlet was designed to monitor electrical current being drawn by our devices. If the GFCI detects a ground fault as small as a few Milliamps, which is less current than you will even feel, the breaker will open. This device safely stops the flow of electrical current. I use Ground fault breakers in our kitchen and bathroom per the national electrical code as well as all the outlets in the garage and cellar. Our outside outlets are ground faulted.   Have we gone overboard with GFCI on our home? Not really. Most of them are required by code. As for the rest, I hate to get zapped.
A good rule to follow for your own safety is keep a GFCI between you, your device and earth.  Thankfully, electrocution happens rarely in our homes. Using double insulated devices and GFCI breakers will hopefully reduce electrical injuries to zero.