If someone reads you a long list of random words, you are more likely to remember the first few and the last few than the ones in the middle.
Psychologists call this the serial position effect.
It combines two different memory advantages.
The beginning gets the primacy effect
Items at the beginning of a list often receive more attention and rehearsal.
You have more time to think about them before the next items arrive.
That gives them a better chance of entering longer-term memory.
This advantage is called the primacy effect.
The end gets the recency effect
The last few items were heard only moments ago.
They may still be active in short-term or working memory when you are asked to recall the list.
That gives the final items an advantage called the recency effect.
Why does the middle lose out?
Middle items arrive after the beginning has already claimed extra rehearsal time.
They also arrive too early to still be the freshest information.
So the middle gets neither advantage.
Word number eleven may have done nothing wrong.
It just had terrible placement.
Does this happen only with word lists?
No.
The same general pattern can affect speeches, presentations, introductions, product lists, and other sequences.
Important information placed first or last may be easier to remember than material buried in the middle.
Can the effect disappear?
Yes.
The strength of primacy and recency depends on timing, distractions, list length, and how recall is tested.
For example, a delay before recall can weaken the recency advantage because the last items are no longer sitting fresh in working memory.
Why does order matter so much?
Memory is not a video recorder.
The brain gives different information different levels of attention and rehearsal.
Position changes the conditions under which something is learned.
So when you have something important to say, hiding it exactly in the middle may not be doing it any favors.
A related piece of human behavior appears in Why are first impressions so hard to change?, where the brain handles another everyday judgment or response.
And that’s the short explanation.
Related explanations: Why are first impressions so hard to change?, Why do unfinished tasks stay in your mind?, and Why does time seem to go faster as we get older?