If an asset is expected to rise, people will hoard it given the choice. It's only human to aim for realizing the gains of your most productive assets.
If you convert all of your currency into bitcoin, hunger will force you to spend them, no?
That's why I said "given the choice". Suppose you are the supermarket, they accept both USD and BTC, and you have a portable BTC e-wallet and some dollar bills. After the novelty wears out, rational people will not pay with BTC. And this is why you will never be able to pay groceries in BTC.
Deflation destroys trade.