It is a capital mistake to theorize before you have all the evidence. It biases the judgment. It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. Eliminate all other factors, and the one which remains must be the truth. How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth? We balance probabilities and choose the most likely. It is the scientific use of the imagination.