Question: In a vast majority of the episodes, whenever Mulder and Scully investigate some mysterious or paranormal phenomenon, Mulder believes that some unknown force is responsible but Scully always has a rational explanation for what is happening. In other episodes, when Scully herself is caught up in something mysterious, she is the believer but Mulder is the skeptic. In those episodes, why would Mulder be skeptical about an unexplained phenomenon considering that he a was witness to his own sisters abduction and he saw many strange things that defied explanation while working for the F.B.I.?
Answer: A variety of reasons. Just because Scully saw something unusual does not mean that it was. Mulder always needs concrete proof before he'll believe there's some otherworldly explanation for unexplained phenomena. He's too experienced to take a novice's explanation as fact. It is also a plot by device by the writers to switch the tables on the characters to make it more interesting and to let viewers see another side of their relationship.
Question: Why do Power Rangers series reuse original Sentai fight footages instead of filming new footage?
Answer: As he stated many times throughout the series, Mulder needed Scully to be sober and skeptical. Whenever Scully's skepticism wavered and she started questioning her own rationality, Mulder would try to restore her sense of skepticism, because he needed her to be clear-thinking.
Charles Austin Miller