Exactly. I fail to see why that is difficult to understand. Volatile = unstable by definition
So USD is not a stable store of value.
Within one or two hours, the USD price went up from 1.4 mBTC to 1.9 mBTC, and now down again. That's extremely volatile!
Yes, but while you are able to buy a loaf of bread for around $1.50 and that price remained the same during those couple of hours, the same purchase in mBTC just went from 2.1 mBTC to 2.85 mBTC.