Guesswork is what you do when you try to find an answer by guessing, because you do not have enough information to know. It is the method — the whole way of working — not one single lucky guess. If a plan is based on guesswork, people mean it is weak: nobody checked. Teachers and scientists often set guesswork against real checking: you can start with a guess, but you should not stop there. The word leans a little negative, though actually we all use guesswork when we have to move before the facts arrive.