Professional Answer: A cascading power failure is a chain reaction where the failure of one component triggers the failure of others. In the context of a transmission line, if a fault on one line is not isolated quickly by protective equipment, the power flow will be redistributed to adjacent lines. These adjacent lines may then become overloaded and fail, causing further redistribution and subsequent failures. This domino effect can spread rapidly, leading to large-scale blackouts over a wide geographical area. This highlights the critical importance of reliable protection systems and high-quality, durable equipment.