Speaking specifically about Bitcoin, I found this article (linked below) claiming that nearly 4 million bitcoins are already very likely to have been lost:
According to new research from Chainalysis, a digital forensics firm that studies the bitcoin blockchain, 3.79 million bitcoins are already gone for good based on a high estimate—and 2.78 million based on a low one. Those numbers imply 17% to 23% of existing bitcoins, which are today worth around $8,500 each, are lost.
Source:
http://fortune.com/2017/11/25/lost-bitcoins/I don't know how much of this makes sense, to me the number is simply too high. But, who knows. Another point being made in the linked article is that people are going to be much more careful when sending bitcoins in the future, now that the value of this crypto-currency has been firmly established.
actually the numbers are somewhat near to what can be called lost. Some miners are insane if I may say.
Really. I have read a news back in 2017 where a miner made a mistake or something during the mining of a certain block. They've lost like a hundred thousand bitcoins in a block, iirc.
Correct me i am wrong though. I cannot remember it really. Just the news about some lost bitcoins.