Alcatraz was considered the most secure federal facility in the United States. That reputation created a specific kind of risk: the belief that the security system was doing its job became a reason to scrutinize the system less carefully. Guards who had worked the Rock for years had seen escape attempts fail. They had seen the currents. They had seen recaptured inmates. They had walked the cellblock hundreds of times and found everything in order. That history of things being in order is not evidence that things are always in order; it is a source of the expectation that things will continue to be in order, an expectation that reduces the intensity of observation.
The men exploited this expectation across every phase of the preparation. The music hour drilling worked because music hour existed for a reason, and guards had learned that music hour meant noise. The cardboard panels worked because guards had learned that the walls were walls, and a wall that looks like a wall is processed as a wall. The dummy heads worked because guards had learned that the shapes in the bunks were sleeping prisoners, and a shape in a bunk that looks like a sleeping prisoner is processed as one.
None of these individual failures is catastrophic in isolation. Each represents a reasonable heuristic — a mental shortcut that works the overwhelming majority of the time. The escape required all of them to work simultaneously. It required months of observation and preparation to set them up. It required coordination among four men to execute.