From the article:

Parsons said the fault had been traced to the installation by a contractor, Hamilton Sunstrand of Rockford, Illinois, which had reviewed its procedures and found there was nothing to prevent the gears being installed backward.

According to some articles I've read, the original definition of Murphy's Law was "If it can be done wrong, it will be done wrong."

Over 50 years after the publication of Murphy's Law, it never ceases to amaze me how often designers create something that can be connected or installed incorrectly, thus guaranteeing that eventually, it will be done wrong.

Fortunately, many other designers have learned the lessons. For example, take a look at the cables on your computer. Most of them are designed in such a manner that you can't install them incorrectly. That's smart design.

Contrast this with what happened on an Airbus A-320. It also happened on the V-22 Osprey where a connector was reversed, resulting in the 5th prototype crashing on its first flight. Dumb design in both cases.

BTW: This is the best article on Murphy's Law that I've read. It's primarily about a genuine hero, Dr. Stapp, and the rocket sled experiments he conducted to improve safety. Highly recommended.