Electrons are very emotional and compulsive things. They feel
an intense desire to get away from negatively charged things or
places, and an equally strong desire to get closer to positively
charged ones, as if according to some law of nature.
By means of chemical things inside batteries that I don't understand,
one end of the battery is kept positively charged and the other one
negatively charged. So if there's anything between the terminals that
an electron can easily flow through, they'll do it !
