No one size fits all
In the late 1940s, the United States air force had a serious problem: its pilots could not keep control of their planes. Although this was the dawn of jet-powered aviation and the planes were faster and more complicated to fly, the problems were so frequent and involved so many different aircraft that the air force had an alarming, life-or-death mystery on its hands.
After multiple inquiries ended with no answers, officials turned their attention to the design of the cockpit itself. In 1950, the researchers measured more than 4,000 pilots on 140 dimensions of size, including thumb length, crotch height, and the distance from a pilot’s eye to his ear, and then calculated the average for each of these dimensions. Everyone believed this improved calculation of the average pilot would lead to a better-fitting cockpit and reduce the number of crashes — or almost everyone. One newly hired 23-year-old scientist, Lt. Gilbert S. Daniels, had doubts.
So when the air force put him to work measuring pilots, Daniels harboured a private conviction about averages that rejected almost a century of military design philosophy. As he sat in the Aero Medical Laboratory measuring hands, legs, waists and foreheads, he kept asking himself the same question in his head: How many pilots really were average?
Out of 4,063 pilots, not a single airman fit within the average range on all 10 dimensions. One pilot might have a longer-than-average arm length, but a shorter-than-average leg length. Another pilot might have a big chest but small hips. Even more astonishing, Daniels discovered that if you picked out just three of the ten dimensions of size — say, neck circumference, thigh circumference and waist circumference — less than 3.5 percent of pilots would be average sized on all three dimensions. Daniels’s findings were clear and incontrovertible. There was no such thing as an average pilot. If you’ve designed a cockpit to fit the average pilot, you’ve actually designed it to fit no one.
Credit: When U.S. Airforce discovered the flaw of averages

Once they identified the problem, the air force engineers came to the solution quickly — adjustable chairs. This eventually led to flexible car seats.

When we design software products, we think about an average customer or an ideal customer. But the reality is that there is “no ideal customer”.

Seth Godin in an episode of his podcast — Akimbo, discusses the personal attention each user expects. Every user expects that the product or service to work flawlessly for his or her requirements.

We, software developers, expect the same attention while we use other products. But when we develop software, we ignore the “personalisation” and build it for an ideal user 😄.

Know your users well enough to avoid the “ideal customer” trap. Keep conversing with them, observe them. Otherwise, we end up developing for the average, which is hardly anyone.