system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why did doctors and scientists continue to believe that human health was governed by an imbalance of four humours (blood, black bile, yellow bile, and phlegm) for so long without any supporting evidence?
gpt
There was some decent logic for it, and when cutting people open is frowned upon by your culture its hard to gather evidence to the contrary. 

When you observe people only losing 4 types of fluids and you cant look inside to see whats going on behind the scenes you have to conclude that they play a large part. Over time beliefs  become common place and burden of belief is left up to the opposition. Once autopsies become common place you begin to see an increase in medical science.