I have not lost any of my holdings of Bitcoin or Altcoin by doing anything wrong. But many may have lost their holdings of Bitcoins or Altcoins due to their own mistakes. But there are also some reasons to lose it, one of which is to keep the wallet seed invested carelessly. There are many people who join various airdrop campaigns with their invested wallets who work on all these campaigns and connect the wallets with seed phrases to claim tokens and as a result they lose their holdings. But the safest system for keeping seed phrases is to write the seed phrase in a notebook in such a way that no one can ever find your notebook. Thus if one can keep his wallet seed phrase safe then he will never lose his investment.