It's rather easy to assume you know something, especially if it's based on previous knowledge that you are familiar with. And there is oftentimes a level of obviousness in certain things that make questioning particular items unnecessary. But at what length would you go to be 100 percent positive something is true?
The Pittsburgh Post-Gazette recently ran a story on what the paper deemed as obvious scientific research. The items ranged from job satisfaction (a "careful choice of career is the key"), healthcare ("Communication between primary-care physicians and patients can reduce") and power tool usage ("avoid exposing their fingers to direct contact").
While at this time, it would be tough to disagree with any of the above, it seems that some level research needs to be done to determine this. Even the most obvious things sometimes go awry, like the fact that the earth is not flat, or that disco died in the early '80s.