Around the year 1300, the English Franciscan monk, William of Ockham, wrote his eponymous, pithy catch phrase: "Pluralitas non est ponenda sine neccesitate". Which, as all good skeptics know, is now referred to as Ockham's Razor. Of course, Latin may not trip off the tongue these days, so the English translation of "plurality should not be posited without necessity." might be better understood; but even that is still a little clumsy. A more prosaic version is "The simplest explanation is usually the right one", sometimes referred to "The principle of parsimony".
Essentially it requires the investigator not posit explanations that themselves require further explanations. When a Scottish doctor looks for a the cause of a disease where the symptoms could apply to, say, a common cold, or malaria, it is likely they will go with the former unless they suspect the patient has recently been traveling to exotic places. The cold needs no further explanation, whereas malaria does. Is it more likely that the ancient Mayan pyramids were built by human beings, using techniques and systems that, though seemingly amazing, fit within the standards of tools, pulleys, organisation and ingenuity we know humans are capable of; or, were they built by aliens? The former needs no further explanation - we know humans exist and they are capable (even if we didn't know precisely HOW they did it) - the latter needs further explanations galore given that we don't even know if they exist never mind if they are capable.
Of course, the Razor is not a scientific Law that must be applied, nor is it a fallacy to ignore it. It is is a heuristic, a rule-of-thumb that gives us a handy rule to apply when faced with competing explanations. By itself it doesn't lead to truth or the correct answer, but it does help guide the investigator down paths that are useful. It could be argued that the whole enterprise of science is built on the principal stated by William. Scientific knowledge is built, fact by fact upon what is known, so that our knowledge expands and continues to slot together to create a body of knowledge. We don't use the unknown to explain the unknown.