Not sure what you mean. Generally, brute-force cracking of a vault that is protected by a 4-word random passphrase would require a multi-million dollar investment, so no rational attacker would undertake such an effort to crack the vault of a user with a net worth less than 10 million dollars. On the other hand, if the assets protected by your vault have a value in the billions of dollars, then a 4-word random passphrase would not offer sufficient protection — you would need a passphrase consisting of at least 5–6 random words.
Conversely, a passphrase consisting of only three random words could be cracked in about 2 months by an attacker who has invested only $10k in their cracking hardware (and even faster by a network of attackers who are coordinating their efforts). A non-random master password is at risk of being cracked with even less cost.
Thus, unless your net worth is less than a few thousand dollars, it does not make sense to use an insecure (i.e., non-random) master password for your vault.