Keeping coins on an exchange essentially means the platform is "custodying" them for you — if the platform collapses or runs off, your assets could be lost or become inaccessible (the FTX collapse is a painful example).
To reduce risk:
- Prioritize top-tier, regulated, well-reputed major platforms. For tips on choosing, see How to Choose an Exchange.
- Transfer large amounts or long-term holdings to a self-custodial wallet, where you control the private keys. See What Is a Crypto Wallet.
- Don't keep all your assets on one platform — diversify.
A famous saying in crypto: "Not your keys, not your coins."