(fredness), September 2000
So what does the number three have to do with technology and infrastructure? Under the best circumstance it takes at least three simultaneous systems to prove that a new technology can be made reliable. These systems breakdown loosely into the into the following three categories:
Metaphors - cars
Now the car has been an established icon of the 20th century. For over 50 years the basic interface and underlying technology hasn't changed. Why hasn't it changed? Because the car companies and their customers have come to expect cars manufacturers, fuel and service industry to be reliable infrastructure.
A car is reliable if it doesn't break down or run out of fuel. That an industry has grown up out of car owners need for convenient high quality affordable fuel is yet another element of the infrastructure that make cars reliable. Keeping cars from breaking down requires vigilance of the car owner to keep it maintained, or to purchase new when repairs are no longer viable. Servicing a car is simple if it a reasonably common model and/or the vehicle is well understood and has a good records kept about. Usually this is the case with a brand new car - but not necessarily.
My wife and I have three cars. I have a day job that requires daily commutes. My wife has some classes, and other light travel related needs that also require a vehicle. So why three cars?
Cars are complex. Way too complex for any one individual to expect to be able resolve all but the most simple malfunctions that it can develop.
If it is inevitable that a car will develop a major malfunction that will cause it to be unavailable during a time when its services are needed, then an backup vehicle is the only way to hedge against this. This explains the need for 2 cars. Now my wife and sometime both need the services of a vehicle, ergo two primary vehicles and a backup seems to suffice pretty well. And just in case, if two vehicle simultaneously have major malfunctions, a single vehicle can be time shared until major repairs can be completed.
New Technology = Major Malfunction
If a business, family, or individual is considering switching to new vehicle technology for their transportation needs (say going from car to a flying car!) it behooves them to keep two sets of the well known established technology around while they work the bugs out of the new technology. Ergo, three sets of infrastructure are required to prove out an implementation of new technology.
Ultimately a technology become so established and understood so well that it can be deployed reliably in the field WITHOUT A BACKUP! If a car is brand new, it is reasonable to assume that several months may pass without any required servicing (assuming it is driven safely in a low risk roads). New nylon shoelaces are pretty much indestructible for the first few weeks of heavy backpacking. Concrete and re-bar construction will probably withstand most wear and tear for several decades barring nuclear war or freak asteroid.