Counterparty risk, withdrawal habits, account security, and how to tell a trading venue from a casino with a chart.
Money on an exchange is an IOU from a company. Most of the time the company honors it. Occasionally one does not, and the traders who lost everything were not the ones with bad entries; they were the ones who left everything on the venue. FTX had excellent software right up to the day it did not have your money.
Hold on the exchange the margin you need this week. Keep the rest in a wallet you control. Withdraw profits on a schedule, monthly at least, so that a good quarter becomes something you own rather than a number on a screen.
Hardware two-factor authentication, withdrawal address whitelists, and a unique email for the exchange account. Phishing is a more common way to lose a trading account than a bad trade, and it is almost entirely preventable with twenty minutes of setup.
If an exchange's main pitch is 125x leverage, deposit bonuses, and an anonymous company, it is a casino with a chart. Legitimate venues compete on liquidity, fees, and reliability. The leverage number on the front page tells you who the product is for.