Think about how often you blindly inserted a USB A or B (mini-B, micro-B) plug the wrong way first and had to try again. Why is the wrong way even possible? USB C's plug fixes this.

A huge improvement to railway safety was the invention of Mechanical Interlocking. It was made essentially impossible to set signals in some inherently unsafe ways. When you tried to give a Clear signal to the Express, through a junction a late running Coal Train is already crossing, the huge metal lever you're trying to move to do that won't budge because all your controls are connected via elaborate mechanical interlocking to prevent this mistake. The signal remains at Danger, the Express stops, tragedy is averted.