One of the keys to becoming an effective communicator is to understand the limitations of the person you are speaking or writing to.
And one of the limitations that impacts ALL of us is the limit to our short term memory.
One of the most highly cited papers in Psychology is called The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information, which found hard limits to the number of independent items that we can hold in our working memory.
Some people could hold as many as 9 independent things in their working memory, others as few as 5, with most falling right around 7.
Chunks, not bits
One of the fascinating things about this study and others like it was that while the type of thing mattered for your ability to hold it in memory, the length of that thing did not.
For example, while most people can remember at most 5 independent words (as compared to 7 independent digits in a number), the length of the word doesn't make any difference in your ability to remember it!
You're just as likely to remember "Supercalifragilisticexpialidocious" as "Super".
The limits to working memory are in "chunks" rather than some measure of time or bits of information.
Implications: Chunk your content
This fundamental limitation has some incredibly important implications when you're thinking about how to speak or write.
It means that if you have 10 points to make, and you go into them one after another to someone with no gaps or organization, the reader or listener will not be able to follow what you're talking about.
You'll want to narrow in to your key points, ideally 3-5, to give your audience a chance of being able to hold them all in their head.
What if you have more things that you need to say? Create structure — "chunk" your content into a hierarchical structure with groups. If you have 10 things to say, but you can group them into 3 groups, suddenly your content is tremendously more understandable.
The audience can think within a group without running over their memory limits, and then when it's time to consider everything they only have to think about the groups. By "chunking" your content you have taken what might otherwise be an unintelligible mess and made it understandable.