You know what's rocket science? Serial ports.

Every freakin' datasheet states RX/TX but not from which side of the connector. Some look at it from the inside (RX for own receive), some from the outside (RX for receive of the counterpart). But never ever try to explain what is what, that would be too easy.

On literally any first attempt of connecting devices in my life it was wrong. And then you switch 'em and it's still wrong. Then you switch again, and it may work. Or you have to switch a few times more, you never know.

Those freaking bastard interfaces from hell.