Most of us will actually see 3 digits, then 3 digits and 2 pairs of digits. For example (#1): 819-555-1010 (don't worry, it's a fake number).
You probably have read: eight,one,five --- five,five,five --- ten,ten
Why not one-thousand-ten? Simply because our brain is a bit lazy and remembering a large number is harder than digits. But at the same time, our brain is having a hard time remembering more than 3 items at the same time. Instead of memorizing one-zero-one-zero, it's easier to remember ten-ten, that is also easier to remember than one-thousand-ten...
I call that the Rule of 3 and apply it everywhere. When a user is calling for support, I always give them not more than 3 steps to follow and then wait.
- In the menu, click Edit, then Properties...
In the last example (#2), we have the Rule of 3: Menu, File, Properties. Beyond that almost any user will reply with a harsh "Wait a sec, I'm not a pro like you"
Are people dumb? Not at all, we are all limited by this Rule of 3. Some geniuses may be able to handle more, but for us, mere mortals, it's a rule we all comply by.
As a final example (#3), remember the last time your friend told you about his friend's cousin dad that died tragically? Who? For a few seconds you were stuck at figuring the link between the dead guy and you.
- You, your friend, his friend (up to here, it's quite easy)
- You, your friend, his friend, the cousin's friend (we are starting to struggle)
- You, your friend, his friend, the cousin's friend, the dad's cousin (admit it, we are starting to get lost)
Our brain is actually memorizing by patterns. Most often, we'll try to remember by pairs or by triplets. A quadruplets is easier to remember by thinking of two pairs. A quintuplets is easier by using a pair and a triplet...
You get the idea.
When providing support, always remember this: never more than 3 steps at a time. The same rule applies when designing code or a new user interface. Never use more than 3 parameters to a function. Never nest a sub-menu further than 3 mouse clicks.
It's a rule that can be hard to follow sometimes. But it's totally worth it as your work will be easier to understand.
There are many more examples I could provide, but I would break my own rule...