Bitcoin is like a cup of sand

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     It is a good analogy. Bitcoin is like a cup of sand,while the sand is continuesly bought  untill it is running out the price of it become expensive because it has only one cup of sand and limited for the buyer. Bitcoin become more expensive if the demand continue to grow while the bitcoin is almost mined and limited to 21million.
     But bitcoin and gold is different in usage even they are both valuable. This two are need by the people in different ways.