Bitcoin is not a valid currency because bitcoin was created not to be a physical buying and selling tool, whereas our real life is the life in which we transact in real terms like for example: we buy shoes with legitimate money / currency. We live in the real world not digital nature hhehehehe. And why is bitcoin not good as a currency because of the price of bitcoin itself can be said to be unstable, where the nominal value of 1 can change every second. While for example the dollar, it is clear the count.