6. If you lose your bitcoins they are gone forever
So, we will never have 21 millions of BTCs circulating on the internet. That means even more we will have less Bitcoins on the world. What I like about it, is that BTCs will become more and more valuable, probably the demand will surpass the offer, making little satoshis costs a lot.
But, the disadvantage on it, is that Bitcoin can decrease a lot its amount on a distant future, making this coin a ''relic'' of our time.