Sure, both theories are possible, but which is more likely? William of Ockham--the creator of Occam's Razor--would argue that, all things equal, the simplest of explanations is most likely when given the option of choosing an alternative containing many hypothetical additions to the evidence at hand. Occam's Razor is used to point out that conspiracy theories are generally nonsense.
Theory B: I came home from school and my door was unlocked. It was unlocked because, after I locked it and left for the day, my neighbor ran out of sugar while baking a cake. To get some sugar, she climbed the tree between our houses, hopped onto the roof, crawled through a window I left open on the second floor, took some sugar, and left through the front door, forgetting to lock it on her way out.
Theory A: I came home from school and my door was unlocked. It was unlocked because I forgot to lock it when I left in the morning.
Which of the following theory is most plausible?
"non sunt nultiplicanda entia praeter necessitatem" (i.e., "Don't multiply the agents in a theory beyond what's necessary.")
Hickam's Dictum
To be fair, we need to acknowledge Hickam's Dictum, which is a counterargument that surfaces in the medical profession. It is true, that in some cases, the obvious answer is the wrong answer, and more obscure possibilities end up being true. For example: A patient shows up with a high fever, body aches, and a headache, an M.D. might logically conclude that this person most likely has the common cold or influenza. They would be right most of time; however, every once in awhile it's caused by some strange, even unheard of, amoeba that eats brains. It could even be a combination of multiple medical issues working together. As Hickam said, "A man can have as many diseases as he damn well pleases."
Adapted from: Dr. L. Kip Wheeler 1998-2012. Permission is granted for non-profit, educational, and student reproduction. Last updated March 30, 2012. http://web.cn.edu/kwheeler/fallacies_list.html