Yes it is basic knowledge. We must keep the amount we have on the exchange to be able to trade. sometimes some exchange does not offer good security features and even the exchange can make an action that is not commendable by taking over the account we have. every time we entrust the amount we have on the exchange then we must be prepared to face the bad risks occur. Security is only guaranteed when we can save the amount we have on personal wallet, especially is an offline wallet that has a private key security feature. Each coin must have a wallett official and it is the safest option to date.
That's why even if you're a trader or long-term holder then you should not put all your funds on a certain exchange/web wallet, don't invest/trade what you can't afford to lose. Because any sites are too vulnerable to hacking.
Trading with individuals on forums etc. is another option to avoid using centralized exchange.
This might be a good option but be careful and be aware to whom you trade with, use an escrow for good.
I'm a FIRM believer that it is ALMOST ALWAYS an inside job when any place gets 'hacked'.
Should I say an exit scam.