Hey there!
The idea of that perfect medium between two extremes was an Ancient Greek idea by someone who was considered one of the greatest thinker or philosopher to ever live. He questioned many ideas and created many of his own that we still use today. His name was Aristotle.
This golden mean, as it was called, was between two large extremes, like humble and modesty, or smart and uninformed. You had to get that golden mean in order to be successful. To the Greeks, this was good news. The ancient Greeks used math as proof there was a God, and another example of proportionality leading to good certainly caused them pleasure.
For example, if you have a lot of things at home, the two extremes would be giving them all away, or keeping them all. You could keep some and give some, and that would the appropriate golden mean.
Hope this helps!
