This is a reading method I learned from another reader. Whenever she does a reading, she throws whatever spread she is going to use and then looks at the card left on the bottom of the deck.
She calls this card the undercurrent. The undercurrent is what underlies the question. It is the atmosphere in which events are taking place.
For example if the querent had a question about a relationship and the 4 of pentacles was on the bottom of the deck, it could be interpreted as someone in the relationship not wanting to let go.
Perhaps for financial reasons (very common), for selfish reasons, or for security reasons. It could be an unconscious or unexpressed desire which the querent him/herself is not even aware of.
Depending on the rest of the cards thrown, letting go might be the best thing. I find the concept useful and use it in my daily readings.