I am a fan of old 8-bit computers, so when I found an original TRS-80 in the surplus electronics store where I buy things like stepper motors, I had to take it over to the test bench and see if it actually worked. It did power up, but while I was connecting it up, I discovered this:
There are three connectors on the back of the keyboard unit which are labelled, in raised black-on-black letters, TAPE, VIDEO, and POWER. All three are identical 5-pin DIN connectors. This means that any of the cables will fit into any of the connectors. And they are on the back of the keyboard, so you're very likely to be plugging them in blind, by feel. This means the chance of plugging the wrong cable into the wrong hole is pretty high.
As with all consumer products, the engineer that designed this computer was desperately trying to keep the cost as low as possible. By using the same connector, there was only one unique external connector part number on the bill of materials, so their purchasing volumes for that connector were three times as high, meaning they get better volume pricing. They also needed to create only one connector footprint symbol for the printed circuit board. But from a human factors point of view, this is a terrible decision. It is absolutely certain that people are going to plug the wrong cable into the wrong connector sometimes, and their computer would be mysteriously not working. Indeed, depending upon the pinout of the connectors, the computer might even be damaged. If it is still under warranty, they'll be angry and demanding of a repair, replacement, or refund. And if it is out of warranty, they'll be angry and they'll tell all their friends about your terrible quality.
When you design something, it's important to think carefully about all the ways it could be used incorrectly. You can't always outwit someone who is determined to do something wrong, but you want to try to make the correct way of doing things the path of least resistance.
