Part Two: The product · Everyday use
It is simplest to build for a desk, a large screen and a good connection. People reach for the product on a phone, in a queue, with one hand.
Picture a building inspector on a roof. He has a phone, work gloves, bright sun on the screen and one bar of signal. The inspection software was designed at a desk. It has a twelve-column table and small buttons, and it cannot save without a connection. So he writes on paper and types it all up at home that evening. The product has given him a second job.
Indoor work has the same moments. A parent books a doctor's appointment at a bus stop, holding a child's hand. A manager approves expenses in the two minutes between meetings. A nurse uses a shared computer that someone else was logged into a moment ago. A warehouse picker scans with one hand and carries with the other.
Makers build at desks, on large screens, with fast connections and time to concentrate, and they test in the same place. The product fits those conditions because nobody on the team has ever used it in any others.
Not everything has to work everywhere. A long report may be desk work and can stay that way. The tasks people do away from the desk are usually few: look something up, write something down, say yes or no. Those few have to work completely. They need to fit a small screen and one hand. They need to keep what was typed when the signal drops, send it when the signal returns, and say which has happened.
Therefore:
Find out where people are when they reach for the product, and what they have free: which hand, how much screen, what signal, how long. Make the few tasks they do there work completely.
In practice. Take your phone outside. Start the product's most common task with one hand, and switch on airplane mode halfway through.
Goes with. Where people are is learned through WATCH WHAT THEY DO (20). A lost signal must not lose the work, which is NOTHING IS LOST (55). One hand in sunlight is a temporary case of WORKS FOR EVERY BODY (60).