My most important crypto advice is "not your keys - not your coins" because it is simply a very important advice, where we should be aware to have real access to our coins and don't need to rely on a middleman.
Not your keys, not your coins video from Andreas Antonopoulos.
Security checklistReminder: do not keep your money in online accountsBitcoin is clearly designed as a P2P currency.
It is about transactions but with private keys, you have control on your coins and your transactions too, full controls. You can use P2P exchange service but if you don't have private keys, you don't control your coin and transactions, hence you have to rely on that P2P exchange service.