My biggest mistake was the excitement that altcoin brings, and instead of focusing on Bitcoin, I went to focus on altcoins. During the Crypto Winter of 2022, I realized that it was completely wrong. I pivoted back to Bitcoin after that, to recover from my losses I made. Since then, if people had asked me what was my lesson, I would tell them to focus on Bitcoin instead.

Well, I have a real experience. I was being scammed by many cloud mining sites and investment sites but the good part is that they are the reason why I ended up being here on the forum because I never knew that there was a Bitcoin forum because usually I am in programming and coding forums where the earning section talks about faucets until I also try those cloud mining sites and mining with GPUs.
I thought at that time I could be rich fast because of the cloud mining site because most of the people on the other forum said it is legit and the daily mined coins are really high, but in the end I'm being scammed by them.

However, I still feel lucky they pointed me to this forum and learned more about them, including mining BTC and mining other coins.
Those are my newbie mistakes. I was attracted to cloud mining offers and investments that need to be avoided nowadays because there's no investment or cloud mining site that's legit except the offer from Binance and renting service from miningrigrentals.

For new Bitcoin user, it could be FOMO, entering in the bull market. And so when the price decline in the next cycle, you panic, you sell at a lost and then said to yourself that it's the worst investment you have. But you really didn't do your homework as you just read the news and then FOMO about it. So you really need to do some research in the beginning.

And obviously the best resource is this community. Maybe at the start you didn't find it. But for me, if you are going to involved yourself in Bitcoin, it's a must to join our forum and explore and read from the past experience of users here who have been ahead on us in the market.

One of my biggest mistakes years ago was skipping my non custodial wallet whenever I had to convert my crypto to fiat. It started with one gambling site to save on the fees and slowly became a habit. I overlooked the risk of skipping that extra step and paid the price by losing my account at one of our best local exchanges at the time.

With so many posts and threads about this issue, the only thing i'd say to the new guys is to take note or use the search bar on the side because it's easy to forget the helpful stuff we read here.

Personally I find it difficult to pinpoint a single biggest mistake because there are many things of
equal importance which can lead to a mistake, here are a few I can think of: _{in no perticular order}

Self custody: For the sake of a $50 hardware wallet, it makes a lot of sense to be in full control
of our coins, instead mistakenly relying on a third party to hold the coins.

Trading: Because Bitcoin and crypto are so accessible many newbies think think they can "hit the
ground running" and start trading with no knowledge other than watching some random
influencer on YT with 500k followers.

Expectations: Not understanding the movements of the market and expecting it to constantly go up
without a dip in the Bull season or the other way around in a Bear season can lead to FUD and FOMO
and in turn buying or selling at the wrong time.

Most common mistakes made by Bitcoin newbie users are not new, and actually repeated many times by many newbies so such mistakes are all recorded and reminded in some websites.

Cryptocurrency security checklist.
The cryptocurrency scambook.
The dos and don'ts of bitcoin key management.

Above are advice for newbies to start, learn and practice but if they're open minded and ready to learn further, there they go.
How to manage Bitcoin like a whale?

There is no single mistake that we can say is the biggest in Bitcoin that is generally considered as the worst, I think that it depends on the level of our exposures that would determine mistakes that we will avoid, looking at most of the posts here there are different kinds of mistakes that the posters have made. I think we can learn from other Bitcoin holders mistakes to avoid making them rather than wanting to know which of them is the biggest mistake, what you consider a minor mistake can cost you a lot like losing your Bitcoin forever. Every precaution to protect your wallet security should be taken very important no matter how unimportant or irrelevant you think it is. A simple thing like ignoring not to save your seed phrase online can cause you to lose your coins in the case of a compromise online that will affect your stored private information.

There are mistakes made by Bitcoin users in the market. One of them is running or rushing to invest in Bitcoin without having to firstly understand the basis of the market and how entirely it functions. Learn the basis first like the seedphrase, the bull and bear season, the self custodian wallets and how to trigger the buy and sell order in the market, risky management, principles and scams, there are more but these are the important ones a Bitcoin user should know. I would try my possible best to brief these basis.

Seedphrases should not in any occasion or circumstances be share, it's meant to be private that's why it's called private seedphrases. If it's been leaked it means you're no longer the only person that have access to your own wallet because scammers are always there to rip you apart, they know how to devour people and they do it so so well. Another thing is understanding the bull and bear season, know when to buy Bitcoin when the bear season arrived and know exactly how to sell it when the bull season comes. Self custodian wallets are important for sorting and storing our cryptos because more effective wallets have high chances of protecting us from scammers. Risk management is verbal, every investor and trader ought to know  how to manage risks and receive rewards in the market. Principles is definitely the guidelines and more like a disciplinary measures that guide traders and investors, there are some steps they don't take minding the principles one generated. Scams are everywhere and we should try our best to stay off from them because that road is filed with losses.

It's very simple how to make gigantic profits but also technical in the process. It's simple, protect your Bitcoin, then you go ahead and focus on trades and making profits in the market.

The biggest mistake new Bitcoin users make is probably the one that costs them the most money. But that's an individual thing and varies from person to person. For some, it could be losing their coins to a scam or theft, panic selling during their first drawdown, or chasing altcoin pumps instead of quietly sticking to a DCA strategy.

That's a very broad question, and I'm sure everyone has a different experience. As for "hearing real experiences," I think you can find loads of them all over the internet. I'm not really sure we need a new thread for that.