This guy explains why Bitcoin, and any other crypto currency, isn't fungible. Fungibility, for those who don't know, is a property where one unit of something is perfectly equal in value to another one unit of the same something. A dollar is a dollar; the dollar in your wallet buys the same as a dollar in mine does. A five dollar bill buys the same as five one dollar bills in yours, etc. The dollar is fungible.
All crypto currencies are NOT fungible. One bitcoin, which I'll be using as the example but is true of any crypto currency, might have a very different value to another bitcoin. This is because there's three kinds of any crypto currency; regular, virgin, and tainted. Virgin bitcoin is newly mined bitcoin that has no transaction history. This trades at a premium to regular bitcoin. Regular bitcoin is any bitcoin that has a normal transaction history. Tainted bitcoin is any bitcoin which is suspected of having been used to purchase illegal goods and services. Tainted bitcoin can be confiscated by an exchange, and because of this is trades at a discount to regular bitcoin.
The fact that different people can have the same amount of bitcoin but potentially have three very different prices for the exact same amount of bitcoin means that bitcoin itself isn't fungible. The .017 bitcoin in your wallet might be worth a lot less than the .017 bitcoin in mine.
Yet another reason to not invest your wealth into 0s and 1s; buy physical precious metals instead.