Programming Concepts you just "don't get"

[Jonathan Tran <jonnytran@gmail.com>]

It occurred to me that there are many concepts in programming, like
say, monads, that are so obviously hugely important to some people,
but others seem to just "not get" them.  When one of these people that
groks monads tries to convince those that don't   how important the
concept is, they fail miserably, mostly because others have no
experience with monads to relate to.  So how can they possibly make a
judgment of something they don't understand?

This is extremely frustrating for both parties, because the one person
feels they _know_ it's important, but can't seem to get the other
person to see that.  And the other person is kind of bewildered as to
why this person is going crazy over something seemingly so trivially
different from what they're used to.

So I thought that maybe I could try to show these concepts to people
in a way they could relate to.  The reason I'm posting is, I want to
know what you guys out there feel like you either "don't really get"
or "couldn't really explain" in the hopes that I can figure out a way
to show it to people.

Monads are one example, as I've heard from some.  Currying, for those
who are not familiar with functional languages, is another I've
heard.  But what other concepts do you _wish_ that someone would
explain to you (or to others) once and for all?

I'm trying to put together a presentation on exactly this, so your
wish will be my cmd.

Please reply to the list, or to my blog post directly
http://plpatterns.com/post/42929867/programming-concepts-people-just-dont-get#disqus_thread