Why you need to design for the real world.
The story goes that in 1978 a customer wrote to General Motors with a complaint about his brand new Pontiac. He said if he drove to the shop and bought vanilla ice cream his car refused to start.
If he bought chocolate, or strawberry, or any other flavour — no problem. But vanilla? The car just wouldn’t start.
At first the engineers chuckled, assuming it was a wind-up. Eventually they sent an investigator, who accompanied the customer to the shop to purchase vanilla ice cream. And it turned out he was telling the truth: his car simply would not start.
His curiosity ignited, the investigator conducted several tests. He ruled out weather, fuel quality, time of day. Nothing unusual. Until he looked beyond the car itself and went into the shop.
Vanilla was the most popular flavour, so it was kept at the front of the shop. The other flavours were tucked away down the aisles. That meant when the customer bought vanilla, he was in and out in a minute. But if he bought chocolate or strawberry, he took longer.
The shorter stop meant the engine didn’t cool down as much. That led to a vapour lock in the carburettor — a quirk of fuel delivery systems in certain 1970s cars. The problem wasn’t the ice cream flavour. It was that the engine wasn’t designed for short stops: a minimum time needed to elapse between turning it off and back on again.