People are not going to use it to buy grocery, an apple, or a cup of coffee, because it's already easy to use cash to exchange for everyday goods...
But btc can solve other problems, like ... replacing paypal and credit card
Don't people use credit cards to buy groceries, apples, and cups of coffee?
There will be solution for micro transaction like this rather than going into the bitcoin blockchain, like using bitcoin to buy prepaid card etc. I can imagine the transaction fee is set to something high to prevent dust. No, bitcoin won't be the world currency that can live on its own, and has the market cap of all the existing currency combined.