Resistors and other circuit elements can be connected in series or in parallel. Resistance in series circuits is the sum of the resistance.
To prevent the danger of electrical shock and the possibility of electrocution, ground fault interrupts devices detect open circuits to earth ground in attached electrical or electronic devices.
It is difficult for students to understand how electric circuits function. The processes involved are invisible because they occur at the atomic level and thus are abstract in nature. Electricity can not be felt with using the personal senses (unless we receive an electric which is certainly unwanted), electricity cannot be manipulated directly, and what is happening is thus not readily apparent.
The user of the device could become a part of the devices electrical circuit by providing a return path for the electrons through the users body instead of the circuits earth ground. When our body becomes part of an electrical circuit, the user can be seriously shocked, or even killed by electrocution.