system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do companies like Coke gauge the effectiveness of their advertising when it’s everywhere and people buy their products anyway?
gpt
I can't be arsed to find the link, but Coca Cola apparently chose a small target city in the US and stopped all local advertising as a test, and saw a decline in sales.  

It validated the fact that advertising is required to keep the brand in-your-face, lest someone else come along and steal the short attention span of the average consumer.