Currency itself hasn't been created for storing value, but to transact value and by that help the dynamics of economy.
If the currency loses value it's acceptance is reduced for the purpose of transacting. That's why most national currencies can't be used for international trade and global commerce is conducted in hard currencies.
You can't compete with the paypal/$ combo if you are not superior in that regard.
Hard currency - predictable future value
Soft currency - unpredictable future value
Inflation is totally OK with trade, if it is predictable. Inflation/Losing value doesn't make a soft currency, but it's unpredictability is what makes a currency soft and low quality. Just like with bitcoin is a soft currency with a highly unpredictable future value.