Imagine a car battery. They are 12–15V and are capable of delivering 600 amps – when there is a conductor with very low resistance across the terminal. (Volts / current = resistance) so 12 volts/ 600 amps – 0.02 ohms. I human is much larger resistance. You can easily measure yourself with a $10 volt meter. Figure a human is 1 meg ohm or 1,000,000 ohm.
If you connect yourself to a car battery you will only get 12v/1,000,000 ohms = 12 microamps. Nothing.