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.

-Sherlock Holmes in Sir Arthur Conan Doyle's "A Scandal in Bohemia"

Sherlock Holmes might be legendary for his cleverness, but he's not the first person you'd think to go to for business advice.  However, this tip is particularly applicable to making sound business decisions. Fundamentally, he is saying not to make assumptions before researching appropriately.  Often, we tend to go off of our hunches; for example, we assume a client will or won't like something based on our own preferences, past information (which may no longer be valid), or basic logic.  All of these things can lead us astray, however.  We need more up-to-date and direct data before making the decision.  

Sherlock also has a second point for us, too: it's easy to fall in love with an idea or plan once we've had it.  At that point, we tend to have tunnel vision, and even if we then do research, we only really see the information that supports our own opinion.

So if you're looking to make a decision, keep Sherlock in mind, and don't take any guesses as to what to do until you've gathered all the evidence first.  Look at the data first and then brainstorm solutions, not the other way around, and the process of making the right choice will indeed be "elementary."