My friend and extraordinary inventor Tom Chi keep reminding the participants in his fantastic workshops and talks to end the guessathons. Guessathons are those moments when a bunch of (often smart) people get in a room and spend all their time and energy with arguing about their guesses. This spans anything from guessing about how customers will react to a new product or feature to the returns on a marketing campaign or the implications of a new process.
The problem with guessathons is just that — they are guesses, and those often have little to do with reality. Thus every ounce of energy spent or minute discussing is mostly wasted.
Instead of guessing you ought to figure out ways to validate your assumptions — as Tom likes to say: Turn conjectures into actual knowledge in the least amount of time with the least amount of resources.