Thanks guys for your answers , but I still have an other question to ask : according to what you said , bitcoin is going to be rare , right? So its price will be more valuable , won't it?
Value would be more valuable like you said. It will also become rare just because as time pass, bitcoins are being lost due to forgotten private keys, wrong sent btc on wrong addresses or more. Besides it being lost, demand grows as time pass by, adoption rate grows ridiculously fast. Because of the said reasons, bitcoin supply is always decreasing. As it becomes lesser in number because of.decreasing circulating supply, value grows which also helps in it's growth.