A warplane theory of poop

Yesterday I found myself excitedly analyzing my p̶o̶o̶p̶ fecal matter's microbial composition, as one does (in certain circles). And I have a high abundance of this weird Prevotella mizrahii, which I was elated about. And then I remembered Abraham Wald's analysis of warplanes during WWII: the story has been embellished over time but the concept of survivorship bias is very much relevant. When analyzing the damage patterns of warplanes that returned from (=survived) combat missions, it is important to notice that these damages are survivable and that other undamaged areas, such as cockpit and engines, were probably hit in planes that did not return. It makes sense, without pilots or engines, it is hard to return. I am appending a link to a more realistic version of Wald's contribution in the comments. So here it goes: the abundances of microbial organisms that make it into feces do not reflect the actual composition of your gut microbiota. It is possible that my friend P. mizrahii was just a transient passenger that went through and came out for more adventures. Of course we likely shed colonizers as well, the organisms that stay in the GI tract for variable amounts of time, so they too should be detected in the feces at some level, but fecal abundance reflects what "survived" (in quotes because a lot of these guys are probably dead, but the point is their genetic material makes it), not what's in there. So the excitement went down but at least it reminded me of the smartest microbiologist I know, Itzhak!