Cognitive psychologist George Miller found (in 1956) that most people can remember seven chunks of information in their short term memory.
But, you are probably thinking, “there are things I can easily remember that are many more items than 7… And at the same time, some things are more accessible to recall than others. Many people will find it easy to remember things that you find difficult and vice versa. They are easier to place because they are more familiar with those items. They have built up systems and ways of process and recalling them.
Chunking works in a scaffolded way. You can remember things in a context, and you have scaffolded this information so that one item leads to another.

Grouping of related items (chunking) helps us process information.

The practice of User Experience design (UX) can help us process information by breaking down complex info into smaller chunks to enable us to process it, understand it and remember it better.

• Proximity is a common way to group related concepts or items. E.g. Your socks (presumably) live in the same drawer together, in the same general area as the rest of your clothes. You don’t keep one sock in the pantry and the other under a rock in your backyard.
• Meaningfully and visually distinct items are grouped in your mind, even if they live in separate spaces. E.g. When you have a leak in your roof, you can recall all the large water-containing vessels in your house, whether salad bowls in the cupboard or a bucket in the garage.
• Clear ‘visual hierarchies’ help us process and scaffold information. Visual hierarchy is a helpful way that to scale info so we can see what’s important. Hierarchy is why any newspaper, magazine or website has a similar structure. Headings, subheadings, lists and all the visual elements we use are all there to help us prioritise and group information.
• Bolding, highlights, italics, bullet points and numbered lists help us hone in on crucial information.
• Short summaries help us retain vital knowledge.
• Improving scannability is essential. Clear groupings and hierarchies allow us to scan past irrelevant details and jump back to a topic in a sequence when we need that detail again. 

Memory recall isn’t recognition or understanding.

But most things are more complicated than seven items. And our memory far exceeds this small number. But like any sound filing system, any information you can’t recall exactly, you need to know where to find it.
You can have more than seven menu items on a website because we don’t have to remember them; we find what we need to.
That’s good information design in a nutshell. People should intuitively grasp the system you have used to categorise your information and follow it without conscious thought. From computer game design to writing an article to architecture, understanding these systems and building them into your plan is the best way to help your customers navigate it and help them take away the key features.