Cash is basically not a trash because people nowadays are still into earning hard earned cash for their own survival. We are still working 8 hours in a day in order to receive our salary in the form of cash. While we are heading into a cashless society but i believe most of the countries are not yet ready for a big change in the system.
Well, we can't do anything but to use it, the adoption of crypto currencies is still not that huge the reason why we still use cash. But given the situation that they can actually use bitcoin or other cryptos to live, I think they would've proved themselves but right now we have no choice, either they use the trash or they don't use it, at the end of the day all of their cryptos will end up in cash.
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Yes, more likely we don't have any other choice. Since cash is the primary mode of payment, that's why cash can't be considered as trash. Right now, cryptocurrency is not yet adopted/accepted in most countries, but the moment that it will be accepted everywhere, I think cash will be out of use anymore.