You may have heard of the “Bus factor” or the “Truck number”: the number of team members that can be run over by a bus, before the project they were working on must fail. Failure in this case comes because the rest of the team do not have the necessary knowledge to replace the lost members. But there is another way for projects or even smaller tasks to fail: depend on too many things going exactly right.

Homer’s “Odyssey” presents a challenge in which Ulysses has to shoot a single arrow through twelve rings to prove himself. In other words, there are twelve things that must go right — twelve conditions to be fulfilled — before Ulysses can claim to have succeeded. Let’s see this in a less “legendary” case, a user test with participant observation and thinking aloud. I was invited in the test to monitor the process. The prototype, sketched with InvisionApp and accessible over the web as HTML/JavaScript,  was written for a tablet, but was installed on a laptop with a touch screen. The prototype language was English; the test took place in a foreign country, on the premises of a large company who had also recruited the users.

The following is the list of things that had to go right in order for the user test to be completed:

  1. The laptop had to work
  2. The battery had to hold long enough
  3. The prototype had to look the same on the bigger laptop screen
  4. The touch screen of the laptop had to have the same sensitivity as a tablet
  5. The laptop had to be connected to the internet
  6. The internet connection had to be fast to mimic the expected speed of the interaction
  7. The users had to know English

You can guess what happened:

  1. The prototype buttons and text looked tiny and unreadable on the laptop screen
  2. The touch screen had to be pushed way too hard to register the touch
  3. Company policy did not allow non-company devices (i.e. laptop) to be connected, so a phone hotspot was used instead.
  4. The phone connection was so slow that a delay of 10 seconds occurred for every button press
  5. The English level of the users was dismal

Inspired by Ulysses and by the above story, hereby I propose the “Rings Factor”, defined as “the number of conditions that must be met in order for a given task to be completed successfully”. The higher the Rings Factor, the less likely success is. A system with tightly interconnected parts, where all must work in unison to complete a task, has a high Rings Factor and high failure probability. A loosely coupled system where components can work independently has a low Rings Factor. Any component failure will impede some tasks, but the rest will succeed unhindered.

The Rings Factor of the user test above is 7. Translating the prototype in the users’ native language, downloading the InvisionApp prototype as a bundle, and putting it on the tablet brings the Rings Factor to only 2:

  1. The tablet has to work
  2. The battery has to hold long enough

Moral of the story: Unless you are Ulysses, stick to a low Rings Factor.