I've got a couple of mistakes. Let's start with these two.
#1; I was in the need of money and I sold a part of my BTC at what I thought was the right moment. Later it turned out that that was one of the worst moments to sell BTC..
If you really in the need of that money, I think thats not a mistake imo. And no one can predict accurately about what will happens to bitcoin in future. So thats not fully your mistake.
my worst mistake with bitcoin was sending 0.15 bitcoins to a website that turned out to be a scam
My friend lost around 4 btc in a mining website, he was desperate at that time. But he have recovered all in gambling lol. Cant expect where he got that lucky. Atleast a mistake can give you an experience, so you wont repeat that again.
Moving 5 btc to a cold storage, but due to computercrash losing the password and thereby losing 5 btc
And no, I'm no whale, so this was ALOT of bitcoin for me sadly
Well it has been a warning for us, to make the backup of our passwords so we cant lose it if our computer get problem. 5 btc is a huge amount dude, sorry to hear that.