Customers do not want your product. They have something they are trying to get done, and your product is one way of getting it done. Understanding the job explains behaviour that demographics cannot.
The classic illustration is the milkshake study: a chain wanted to sell more milkshakes and studied who bought them. Segmenting by customer type produced nothing useful. Watching *when* they were bought found a large morning trade — people driving to work, hiring a milkshake to make a boring commute less dull and to stop them being hungry until lunch.
The competition, therefore, was not other milkshakes. It was bananas, bagels and doughnuts. And the improvements that mattered — thicker so it lasts the journey, easier to hold in a car — were not the ones a taste panel would have suggested.
Two people with identical demographics hire wildly different products in the same week depending on the job in front of them. The job is stable; the person is not.
The useful question is not 'who is our customer?' but 'what was happening in someone's day just before they came to us?'
Identify the job, then name the real competitive set implied by it. That step is what is being assessed.