In a presentation, i stumbled upon the Statement "JavaScript is a Language everybody uses, yet nearly noone seems to find it neccessary to learn how it works".

And indeed, not many of the programmers i know could explain javascript's prototype concept, or why functions need to be 'bound' to this.

CSS seems to be another example of this behaviour: everyone knows how to put a 'class' to an element, and to write a style .myclass { ... }, but only a few even know of margin-collapse.

My question is: are there more of those languages, technologies, concepts, that are so prevalent that we dont even notice them as something worth learning while we use them?