If the level is millions of dollars, that device could be physically stolen, or some aspect of the cryptography/auth scheme could be attacked through a 0-day.
Of course, it's also possible he just wanted something closer to the convenience of a bank account/credit card instead of a pile of cash and failed in the opsec.
Keep a small amount in a hot wallet for convenience and a larger amount (but not too large) in a cold wallet accessed via hardware. But the bulk shouldn’t be accessible without breaking into at least two lock vaults.
I just love the idea of going around creating accounts at multiple different banks for storing of parts of the key.
Then, when you're finally ready to access you funds, creating appointments at all those different banks, driving to them all, and then finding out enough of the keys are completely missing that you now cannot access any of your funds:
A great success for the idea that your BTC is a store of value not dependent on traditional financial infrastructure - now it takes the a whole morning and cooperation of 3 banks for you to get at your money.
Shamirs still requires having the (single) private key present for signing.
Multisig is far superior for Bitcoin security. The keys can remain geographically separate at all times. Each signing operation requires only the partially signed transaction (PSBT) and the other public keys.
Non-issue if you only use the key once, then do a new split each time. Plenty of tooling exists to make this easily in reach with a simple shell script.
Why would you use Shamirs when the Bitcoin protocol has a superior mechanism built in?
SSS is a good solution for other key material, and for storing a paper key to be used for recovery purposes, but it's completely inferior to multisig for normal management of a shared and/or large Bitcoin wallet.
For me as a consumer, storing money in a bank is far simpler and more convenient and more likely to not get me burned than it is to store various hardware tokens with various banks (having to physically retrieve them when I actually want a purchase).
So, if the only way to secure BTC is to this cold wallet dance, then it's clear BTC is not a usable store of value compared to USD.
No, I was attacking your idea that it's somehow common sense that the best way of storing BTC is by working with multiple banks (!!!) to store various key fragments, by showing a more extreme version.
Of course, if someone did follow your example, and then the government compelled the banks to hand over access to the physical tokens, other people similar to you would come out and say "not your keys, not your bitcoin", or insist on even more byzantine forms of secret protection.
Not to mention, with your proposed scheme, actually using your BTC becomes significantly slower than any international bank transfer.
“Targeted attack” can mean many things. If you have control over wast sums of hard to trace treasure a determined attacker might just kidnap you and/or your loved ones, and win your cooperation using threats of violence.
Your suggested safety precaution is a sensible start, but far from enough if you have a lot of bitcoin.
Not really. The device used to sign transactions should never be connected to the Internet.