1: You can see that from the
experience of those who stored their Bitcoin on
exchanges such as FTX and the rest of the other crashed
exchanges.
The first rule of investment also says invest in those assets of which you have knowledge about or if not gain knowledge for them and then invest your money into it.Those people who ignore it invest in hope to earn some quick profits but when it's not happening they start panicking calling it scam or ponzi selling their coins which is a mistake.
Secondly the biggest issue is keeping your funds on these CEX who are in actual possession of your keys through which they can easily spend your funds so you are not owning any bitcoins if they are on CEX so take it out and store them on hardware wallets or non custodial wallets like Electrum with safety of your seed phrases.Learn more about wallets
here3: Dont hold alternative cryptocurrencies for the long term
and if you must own them just know you are just
gambling with your money, because they can go
from100 to 0, so altcoin is worthless for the long term.
On the contrary I would say if you are newbie then investing in shitcoins is the biggest mistake you will make in hope of diversifying your portfolio because bitcoin is the only best option for you while those altcoins are pump dump scheme to make profits for the whales only.You can check on CMC how top-10 have changed instead of bitcoin which remains always at the top.The main reason behind it there's no utility for these altcoins so no long term price surge but if you can trade it short term you can give it a shot but as newbie stay away from it.