Generating secure private keys or mnemonic phrases requires high-quality randomness. While card games may provide sufficient randomness for casual use, they fall short for cryptographic purposes. To achieve a secure entropy of at least 128 bits, one must draw cards randomly 128 times, a process that human shuffling may not reliably achieve. Dice rolls offer a better alternative, requiring at least 50 rolls with fair dice to meet the minimum security entropy, as 6^50 exceeds 2^128. For those seeking true randomness, professional services using atmospheric noise are available, though they require trust in the provider. Ultimately, for generating secure keys, it is advisable to use established solutions like reputable hardware wallets, unless one can create a secure environment independently. This approach minimizes the risk of security pitfalls.