When McDonald's hired disruptive innovation theory pioneer Clayton Christensen to improve milkshake sales, they identified half of their milkshakes sold before 8.30 am.
It was the only thing those customers bought, they were always alone, and once they bought it, they drove off with it.
When Christensen's team confronted those people about what job they were hiring the milkshake to do, they struggled to answer.
To help them understand, they asked them what else they hired when the Milkshake wasn't available in a similar situation?
So they answered doughnuts, but they could never buy one.
Another person said bagels, but it was dry and tasteless. So they'd have to put cream cheese on it whilst steering the wheel with their legs.
And another said that they hired a banana, but you could finish it in under a minute.
The McDonald's Milkshake was doing so well because it took 23 minutes to suck up the liquid using a thin little straw.
The job that these people were trying to get done was that they had a long and boring drive to work. So they needed something to be engaged with life while they were driving the car.
From the customer's point of view, the job was accomplished better by the McDonald Milkshake. Why? The thick viscous nature of the Milkshake made it difficult for them to suck up the thin straw.
If they were to change the Milkshake's to have a thicker straw and thinner liquid, it would instantly fail the customers' job, and they'd move to the next best option.
And that's how customer's see a successful product.