Why Mixing Positive and Negative Wires Can Ruin Your Electronics

Not just in fpv, but in all electronics. It is so strange that a powerful, valuable, expensive(or cheap, doesn't matter) board can be trash in seconds by just mixing + and -. Today I was making a project with esp32(outside of fpv) and accidentaly mixed those two cables and in seconds the board was burned. I know it is a normal thing, i know there are some components that prevents this from happening but i think it is strange that it can be nothing but trash(or maybe a soldering test board) in seconds.