Saying a bitcoin is worth x amount of
You comparing something to nothing (a made up number on a printed piece of paper)
Now lets compare something to something.
A Joule is a Joule, 10 years ago, now, in the future. The value of bitcoin changes because things happen.
And that is essence of money and gold. Pieces of paper and shiny metal rock. They have a value only because people want them. Their role is to make trade and transactions flow. Imagine how irritating life would become if we had to barter for things we need. Problem lies with hoarding money and using interest to unbalance that flow.
There has been a strong need for an internet currency without borders and bitcoins has filled that role. You can't argue with how much easier it would be if you could buy and sell everything online with bitcoins.