But even though I don't have hardware wallets yet, I don't just keep it in one USB flash drive, but in three USBs so that in case of loss or damage, I have another USB flash drive reserved.
Besides that this is a flash drive waste, what will happen if all three flash drives die approximately at the same time? It's an existent concern, much more probable than losing three pieces of paper at the same time, if you're cautious at least. And it's even more probable to happen if you have bought all three drives at about the same time, given that they have the same lifespan.