The engineer was bored.
His latest product was sailing through manufacturing, no surprising hitches or glitches to resolve, and he came to work each day wondering what to do to keep busy. Management and Marketing had not yet decided on the new projects, and so he had a couple months of free time on his hands. With nothing better to do, he spent a few days dreaming up a serial backplane interface based on passive directional couplers to provide slot-to-slot port isolation.
As far as he knew this had never been tried before, and he was curious as to whether or not it would actually work. With this technique a multiple-slot, high-speed serially-encoded data bus would not be susceptible to loading variations caused by filled or empty card slots, and each individual card could include true end-of-line matched termination instead of forming an open stub. The bored engineer rummaged through his junkbox and pulled out several directional couplers left over from a previous defunct project.