I'm having trouble understanding what you mean.
I mean, you don't go to the store and have them expect you to figure out the price of the product, taxes and exact change by yourself.. you know?
Why would it work any differently with Bitcoin?
If you're doing a friend to friend transaction most wallets tell you the price or you can look up the exchange rate yourself.
For example, what if you were in a Coffee shop, and the cup of coffee costed .000125 BTC
The average person would not want to waste time squinting at the decimal places and figuring up how much it actually is. Of course this is just my assumption that ordinary people would not want to do the math in their head all the time. I am decently intelligent and even I have to stop and think about it sometimes.
It will likely be priced in a fiat value so you will know how much it really costs. All you need to do is scan a QR code and everything will be done for you so it's not like you have to type in all the decimal places yourself. Regardless of that I think it'll just take some getting used to but people will adapt to it over time.