Kidnapping, torture, etc. Cryptocurrency faces a greater risk of this than traditional assets, since it is so portable and transactions are irreversible. Although other forms of wealth are harder to transfer, we are beginning to see increased ransom demands of crypto assets from targets who are wealthy from traditional assets.
Store keys in multiple locations to increase the difficulty of coercion. The attacker has to steal wallets from multiple locations, require more time and resources and increasing the chance that the attacker will be noticed and caught.
Plausible deniability with BIP39 passphrases.