There are potentially 21 million Bitcoins that can ever be in existence. A lot of people say less because many may have been lost due to early adopters losing hard drives and computers that had large amounts of BTC on them. The amount of BTC you should own at the very least is 0.06 BTC.
In the future once all Bitcoins get printed there will be a shortage of them to go around. Banks are threatened by their existence because they can't lend out deposits of cash through fractional reserve banking. This means BTC will be an asset everyone parks their money into for safe keeping of banks taking control of it and protect it from hyper-inflation.
If you take 21 million BTC and divide it by the US population of 340 million people you get about 0.06 BTC for every American. With the US being a very small part of the world's population you'd be in the 1% with 0.06 BTC if it becomes the world's reserve currency.
There are about 7 - 8 Billion people, and many of them don't own any BTC. The likelyhood if major players and investor try to hop into BTC over the next few years will shrink the supply. You will be safe if you get 0.06 BTC then you will be far better off than people who don't have BTC.
Right now 0.06 BTC is about $552. If BTC hits 10 million dollars per Bitcoin you would have $600,000 and be way better off than your peers. And if you live somewhere cheap you could probably retire off of that BTC. Buy a cheap house in the Mid-West of the USA for $100,000 and just live out the rest of your days in comfort.
Banks are threatened by BTC because they won't have access to your funds to be able to lend them out to others in fractional reserve banking. A bank takes your $100 deposit for safe keeping in your Checking or Savings account. The bank then lends out $90 to someone from your DEPOSIT to a person trying to buy a house or a car. Now if this person doesn't pay the loan back the bank doesn't make any money and they are losing money. They did this with the housing crisis in 2008 and now with student in the US and hyperinflation in Turkey, Argentina, Venezuela, and economic troubles in Italy it is only a matter of time before banks and governments destroy the financial system.
At some point in your life you should own 0.06 BTC and you will part of the 1%. If you don't and BTC goes to zero you lost $552 or so, but that's a a gamble I'd be willing to take everyday of the week.