When you know a lot about a certain subject, you forget how little everyone else knows, or cares (even other experts). So you’re more likely to explain something too fast, or in too much detail, or use complicated language: to you, it’s all obvious and easy to understand.
How do you avoid it?
Write for an intelligent non-expert: you don’t need to patronise them, but don’t blind them (or bore them) with science either.
Where can you learn more about it?
We like how Harvard psycholinguist Steven Pinker explains it in The Sense of Style.