I don't think it's a high number. It could be even higher imo. You have to remember that big big chunks of all coins were mined in the first few years. In 2010-2012 people used Bitcoin very differently - so much just got lost to people throwing their old laptops away.

tomlaies

Many people say that the lost bitcoins are more or less 4 million due to on-chain analyses, that is, those 4 million BTC have been immobile for too long, if so, it agrees with that percentage, but I also doubt that those 4 million are lost, many times some old wallets of more than 10 years are reactivated.

riberet19

bitcoin_beginners

Question on the 17.6% lost BTC

alashazam

I don't know about 17.6%. That seems like a high number unless you count Satoshi's coins in that bucket. 

But regardless there is a lot of Bitcoin that has been lost over the years and just adds to the limitedness of supply. 