Every experienced crypto investor has a story about an expensive mistake. Bought at the top. Fell for a scam. Lost a seed phrase. Sent coins to the wrong address. The list is depressingly long and remarkably consistent — the same mistakes happen to different people, over and over.
The most expensive mistake most beginners make is buying during peak excitement and selling during peak fear. It feels rational in the moment — prices are going up, so you buy; prices are crashing, so you sell. But that's precisely the opposite of what builds wealth. You end up buying high and selling low, repeatedly.
Close behind that: security mistakes. Using the same password everywhere. Leaving large amounts on exchanges. Not having a hardware wallet. Clicking links in suspicious emails or DMs. These are all avoidable with a small amount of effort and knowledge — which is exactly why they're covered here. The other major category is over-diversification into speculative altcoins — putting money into dozens of projects hoping one will "moon," while lacking the knowledge to evaluate any of them. Simple and boring often beats exciting and complex in the long run.