For example, it is not advisable to keep cryptos in exchanges because it increases the chance of your crypto been stolen.
It also not advisable to keep cryptos in devices you are not assured of very high security. It is best cryptos are kept offline (cold wallet) than online.
Right, self-awareness, knowledge is the key here to at least prevent this kind of things to happen to us. That's why the advise you have give should not be taken lightly even by crypto enthusiast who have been in the game for so long.
That's why services like hardware wallet is advisable if you have a lot of coins to hold long term as not to exposed it online. This is part of being a coiner, you really have to learn how to protect and secure it.