Many people regret that they did not buy BTC while they first knew about it. For some, they did not sell BTC while they could. 
For me, I got MWC & HEX for free from airdrop to BTC HODLers, but dumped them before they peak. I could easily make 10x of my existing BTC, if I held them strong.
What is your Biggest Crypto Regret?
Like most of people here my regret is to not buy the top coins when they were really cheap around march-april of this year especially due to covid 19 when we saw a big crash in the market i still remember how big the coins dumped and later they recovered quickly in few weeks so not buying at that time is kind of regret because it was great opportunity to buy.For me, I got MWC & HEX for free from airdrop to BTC HODLers, but dumped them before they peak. I could easily make 10x of my existing BTC, if I held them strong.
What is your Biggest Crypto Regret?