If a fiat currency is destroyed, money could be printed to replace the lost supply. In the case of BTCs however, the number of BTCs that will ever be “printed” will, at most, be 21,000,000. Additionally, there exists no central authority that can decide to “print” more BTC because someone say, failed to care properly for their wallet.
Nobody can ever be sure what quantity of BTC has been lost forever but surely some has. I lost a small fraction of 1 BTC when I failed to do a backup. Is this a drawback for BTC? The currency can be broken down to extremely small fractions, so there should be no worry of running out of BTC. However, the network can’t verify when BTCs have disappeared and can no longer be supplied. Is the fact that the amount of BTC in circulation can only be estimated a disadvantage of BTC?