"If you can't explain it simply, you don't understand it well enough." - Albert Einstein
This quote annoys me. I've spent the last year trying to understand functional programming and this deep, mathematical concept called the monad. It turns out that monads are simple to explain: if you're mathematically inclined and know your category theory, they're a monoid in the category of endofunctors. If you're a programmer, they're a pattern for the augmentation of function composition.
But it took work. It took a lot of work. Even with twenty years of software engineering experience, it took hours of hammering away at the problem, day in and day out, for me to even start to see the benefits of using this pattern. I've now got a fairly solid understanding; I'm hoping to apply it to some personal projects in the hopes of reducing my error rate and speeding up delivery.
Lots of people have tried to "simply" explain monads to me. But to understand them, I had to put in the effort. I had to put in the hours. I had to do the work. Sometimes, no matter how well you understand "it", no matter how simply you explain "it", your audience simply doesn't have the knowledge, the mental framework, necessary to understand what you're talking about.
And some people, no matter how hard they try, will never have that framework. They don't have a mind capable of grasping it. We would never ask Sarah Palin to try and understand multi-dimensional vector maths; she hasn't got the mind or temperance for it. It's not even that she won't, it's that she can't. By nature or nurture, she hasn't got the headaround for it, and never will.
It's not about understanding or simplicity; it's about your audience's capability and willingness to comprehend.