Once upon a time, all the dogs gathered, to discuss about how to avoid traps from the mean and angry farmer so they can eat fresh chickens from his farm. After several suggestions had been debated, a dog said, "How about let's all go out to look for the traps and come back?" The proposal was applauded. But then an old hound got upon his feet and said, "It's a good idea, but how do you know the exact place of the trap when people come back? What if one of us were trapped?" Then, a wise dog raised his hand and said, "How about let's all go search carefully and all piss around the traps? That way if any of us happens to get the chicken, he would smell the marks and avoid it. This would work even if he forgot where the traps are at." This proposal was warmly applauded and the dogs got their chicken without injury since then.

Moral: To troubleshoot a system, it's important to know what's needed to be done and have knowledge of the system. However, having proper documentation is more important because it shows not only where problems with the existing systems, but also shows the special information processing circumstances that may not be identified by any other requirements determination technique.