Your private keys are what allow you (or anyone else) to access your crypto. If someone else gets their hands on your private keys, they will be able to access your coins. Also, if you lose your private keys, it may be impossible to recover them meaning that any funds associated with that key will be lost forever and cannot be recovered.
It is essential to make sure that private keys are stored securely in a safe place. Self-custody is the best option for greater control of your funds and better protection against hackers and attackers. TheCoinmama Wallet is a great self-custody option!