Magic number 7+-2
Also known as Miller's law
Memory effect
The 'magical number seven, plus or minus two' is a classic idea from psychologist George Miller that people can hold about seven items in short-term memory at once. Later research suggests the real limit is closer to four chunks, and it describes a limit of memory more than a bias.
In everyday life
A ten-digit phone number is hard to remember as a string of single digits but much easier when grouped into three short blocks.
On your first day at a new job, your manager rattles off twelve login steps once, and by the time you sit down at your desk you can recall only the first few.
Why your mind does this
Our brains handle small, concrete quantities well but struggle with large numbers, fractions and odds. Rounding, grouping and labeling let us make fast decisions without doing the math. For most daily choices, a rough answer is good enough.
Its family, in 30 seconds: Simpler numbers
How to spot it
Notice when you are trying to juggle more than a handful of separate items in your head at once.
What you can do
Use the limit to your advantage by grouping information into a few meaningful chunks, or simply write it down.
Same family: Simpler numbers
SourcesMiller (1956)·Wikipedia