A way to see folders & tags is to treat folders as tags but with the property that items may only be of one folder. The same happens in biology where scientists

A way to see folders & tags is to treat folders as tags but with the property that items may only be of one folder. The same happens in biology where scientists try to classify animals into one folder; a cat is put into the mammals folder (which has multiple hierarchies of subfolders). Instead, this classification system may be much more effective if it is classified as tags instead, where items may belong to multiple folders (or categories). This solves problems like the platypus, which belongs to multiple "biological folders". It seems that humans have a hard time reasoning with the tag concept. I'm not sure where this comes from; is it decades of working with the folder/subfolder idiom in Windows, where most people are grown up with? Is it the resemblance of the physical world where we also put documents into one folder and one folder only? Or is it our intuition to simplify matters, and therefore seemingly make things simpler to uniquely have items belong to one container? I don't know; most likely, it's all the reasons above plus a few that I didn't mention.