How Do They Know?

I love watching people do Tarot card readings, but I am really curious about one thing. I know that the Tarot cards each have a variety of meanings, how do the Tarot card readers know which Tarot card meaning to use in any given spread or any given reading? How do they choose which meaning of a card is most appropriate, especially when they don’t know the person they are doing the reading for? When I have considered learning how to read Tarot cards this is always what has made me think twice. I wouldn’t want to tell someone something totally wrong.