user139906: I set up the Bitcoin Core wallet and set up a passphrase to access the wallet. It seems to be the only way/needed input to access my wallet.
The passphrase was NOT randomly autogenerated as I was expecting. What happens if someone else uses the same passphrase as me? Since it's not random I suspect this is very possible.

user208: The passphrase for the Bitcoin Core wallet is just a passphrase for encrypting the wallet file. It is not a seed phrase from which the key material itself is derived. The keys are derived from a securely generated seed, independent from your passphrase (and not shown to the user).
Nobody can guess your keys unless they have both the wallet file (with the encrypted keys) and (a correct guess for) the passphrase (to decrypt the keys). That also means the passphrase is not sufficient for you to gain access to your funds - you need the wallet file or a backup thereof.

139906: <p>I set up the Bitcoin Core wallet and set up a passphrase to access the wallet. It seems to be the only way/needed input to access my wallet.</p>
<p>The passphrase was NOT randomly autogenerated as I was expecting. What happens if someone else uses the same passphrase as me? Since it's not random I suspect this is very possible.</p>
 208: <p>The passphrase for the Bitcoin Core wallet is just a passphrase for <em>encrypting</em> the wallet file. It is not a <em>seed</em> phrase from which the key material itself is derived. The keys are derived from a securely generated seed, independent from your passphrase (and not shown to the user).</p>
<p>Nobody can guess your keys unless they have both the wallet file (with the encrypted keys) and (a correct guess for) the passphrase (to decrypt the keys). That also means the passphrase is not sufficient for you to gain access to your funds - you need the wallet file or a backup thereof.</p>
