Yes, it is true that the more secure the private key of a wallet, the more secure his wallet is. So of course, these keys should never be left unattended, the more secure you keep them, the more careful you are. I have heard stories of many wallets being hacked, just because the pictures are left unattended and in an unsecured place, many of them get hacked and a lot of money is lost.
So it is best to write down the keys of these crypto wallets on a piece of paper in a diary and keep it in the safest and most secure place.