[omazurov]

That's why there should be another parameter: you should split the key into N parts so that any M <= N can open the lock. You can increase M adding people you don't trust 100%, say to 8, but leave N at your comfortable level, 5. Even if those 3 conspire, they would still be 2 people short of being able to break the lock. You can do 12:5, give 5 parts to your spouse and spread the remaining 7 among your relatives and friends. There will still be a single point of failure, though, if somebody steals all 5 parts from him/her. You can decide to decrease allocation to only 4 parts so that your spouse would need to cooperate with any of the other trusted parties. The point is there is enough room for designing a scheme that is both secure and reliable.