I mean its only 21million btcand there are 6billion people in the world , how can it be enough
It's really enough because every people will not have a big part of the bitcoin, if you can see the other person is buying a gold and you will find he will buy gold with miscellaneous heavy. And every people will get a little part of bitcoin. And every satoshi will have a high value in the future. don't forget 1 btc = 100,000,000 satoshi