Let's assume you recommended the best wallet for him with the said amount of 1 bitcoin to be stored in the wallet because we always have to consider best securities to keep out funds safe first. Perhaps that's better for him of he's to undergo a long term investment.
He then asked if he could store 1 BTC in the wallet, to which I responded, "Why not?" His next question caught me off guard: "What about the saying, 'Don't put all your eggs in one basket'?"
I took a moment to think, but deep down I felt confident in my hardware wallet's security compared to hot wallets. However, he argued that it's best to split the Bitcoin into two parts and store them in two different hardware wallets.
The misconception here's that that phrase "don't put your egg in one basket" signifies that " you should not channel all your expectations such as source of income in just one place". Which is where the need to diversify your incomes was originated from.
The crypto market is highily volatile so holding such amount of funds in just one source with no other sources can be weird when the market condition hasn't been encouraging for a long time because you might be at need of funds and you selling at the odd time might be at lost to you but when you diversify, you can, if bitcoin market doesn't seem favourable in the moment, some other potential coins you invested on might be of good posture to you and while you splits your assets, you're giving you're expatiating your Incomes to make profits from different sources.
You can't look up to other security lines when you've found an authentic one to say you want to diversify.
Talking about splitting your bitcoin assets of such amount to different wallets doesn't really call on security enhancement but your investment plans which you might want to invest on short and long term goal whereas you don't want to temper on your long term assets when you want to sell your short term assets.