What is rare?

I was in this class on communication systems sometime back , and while describing how mobile companies decide on the capacity of each link , Our professor mentioned "What is rare?".(these companies go by some expectation probability of calls arriving in a certain duration-they want at the maximum only one call to be set up in that duration so that it an be analyzed using Poisson distributions.)

I was lost at this question.Do we really know what is rare?
IITians are rare - at my college ,everyone is an IITian.
Its rare to see a monkey operating the tap at the basin as well as a human-I see it almost everyday!!!
Its rare for me to spot a female(of the Homosapien species) - But I know for sure that almost half the population in this world is theirs.

So our perception of rarity depends on the context.More specifically , it depends on the past registered data.We forget things too!! But somehow , we tend to remember odd or i should rather say rare events.That is because we subconsciously check the newly acquired data with the ones previously registered ones.If we see a connect , it reinforces both the data.But something totally out of the ordinary ,something that has not been registered in the past say 2 592 000 frames (one month, assuming one frame per second) will b3 registered with a flag!!! -And now I bet most of you noticed the '3' which replaced the 'e' but not the 125 of its prior instances on this post.

The illusion of rarity is also used to create value for a certain product which inherently does not have any value ,Eg - diamond.These are mostly of ornamental use and dont satisfy any of the owner's needs except that of possession of something not commonplace.Come to think of it , those De Beers guys must have had the greatest marketing guru decide their policy.

So ultimately I think everything is rare and nothing is.One just needs to "look at things in proper prospective"(Like the secretaries in the series "Yes Minister" would say).