One reason why it’s so tough is that the signal (a smile) is hard to track. The only way to measure it is in-person (or video) testing with real people.
This lack of data was true of most advertising in the old days. So direct mailers that had unfair, early access to data, offered the best insights.
I fear it will be a while before we detect smiles. So to find your framework, you need to identify the people that collect data on delight today. Any ideas who these people are?
