Single Point of Failure

The danger comes from dependency concentration. One account stores information, establishes identity, receives recovery messages, and authenticates access elsewhere. Each additional function makes that account more useful—and makes its failure more consequential. Once the central node disappears, the dependent services can become mutually unrecoverable: you need the account to pass authentication, but you need authentication to regain the account. This is the opposite of Redundancy and Diversification: apparent convenience conceals a tightly coupled system with no independent route back in.

A shared account is not automatically a dangerous single point of failure. The model matters when the dependent functions are critical and no genuinely independent recovery path exists. Duplication also helps only when the backup does not rely on the same account, device, or provider.