Some information may save your life, avoid pain or other issues related to electricity. This energy is clean and very convenient in general but also extremely dangerous so anyone should know how it behaves with the body.
Electricity doesn't move without a voltage difference. Ground is zero voltage and everything above it, like 5V or 500V will cause current.
The body has approximately 100pF of capacitance, like a small capacitor of those usually used to filter high frequency noise or decouple areas of the circuit avoiding DC current. A capacitor then, blocks DC current. The body, with this capacitance, acts in the same way. However, if the electricity finds a path to ground, the body could act as a conductor allowing the flow of electrons, and this means trouble or even death if the voltage is high enough.
That's why having insulation in your shoes has great importance, like rubber. A carpet, wood or materials that don't conduct electricity also avoid this problem. So an informed person is not supposed to touch a possible source of electricity naked or with the wet skin, as this creates less resistance to electricity. Even with shoes on wet concrete or soil.
To have a properly grounded equipment is essential for security in the case of common failures associated with equipment. Audio o video are two main areas for being specially cautious as the user interacts with panels and instruments. A great problem appears when a faulty product that exposes voltage to the user has not a three plug device (with ground) and other yes, or vice versa. When the user touches a faulty device that has voltage potential on it, the body acquires this potential, remember, using the capacitance of the body. If the user touches an earth grounded device the electricity has a path to ground that allows current. This was the cause of electric shocks in the audio field for instance with guitars and microphone stands.
If you do not know how the equipment was connected and you work with electric devices, to carry a multimeter to check the possible presence of voltage in any of item is a very good solution. You know, the red lead in the possible source and the black in something with zero potential. A simple one is not expensive nowadays and it avoids risks.