Causes of dry eye

What causes dry eye? All eyecare websites usually have a list of dry eye causes. However, they're usually not all causes. Many of the things on the list are simply factors that make symptoms worse. And some simply act as triggers for a severe dry eye crisis when the underlying causes were there all along. At the end of the day, it is impossible to differentiate amongst all these things. Most people with dry eye have multiple factors involved, and sorting out which ones are chickens, eggs...