Here is Times Square on New Years Eve.

1
Here is Times Square on New Years Eve.
2
My friend Joe can show me points of interest.
3
Even if theres a crowd (usability). We dont
need exact updates of everyone in crowd
(performance).
4
Heres my friend Fred, who doesnt know Joe. They
appear as ghosts to each other.
5
Nearby ghosts look distinct, but they dont block
my view (usability), and I dont need as careful
synch (performance).
6
Joe and Fred look like nearby ghosts to each
other until I introduce them. I select Joe and
see the operations I can do, such as see him.
7
I select the See Joe icon.
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Abracadabra!
9
I now hold See Joe in my hand,
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which I present to Fred.
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Abracadabra!
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Now Fred can see Joe (usability) and gets
synchronized updates from Joe (performance).
13
Repeating for Fred means that Joe, Fred, and I
can now all see each other even in a crowd
(usability) and only the important
synchronization is done (performance).