Computer Reliability

Deep Thought, the first Magrathean supercomputer, fails spectacularly when it delivers the answer to Life to be 42. While reliable in all other aspects, it delivered and unexpected and unasked-for answer, which makes it worthlessly unreliable. Why the Magratheans trusted it to make its own successor is unknown.

The successor to Deep Thought, Earth fails to deliver the question of Life because it was destroyed moments before the program's end. This unreliability cost the Magratheans millions of years.

Marvin is the servant to the crew aboard the Heart of Gold. He is incredibly smart, having a "brain the size of a planet," with the capabilities of computing extremely complex mathematics, as well as solving difficult problems and operating high-tech devices. Despite this, his depressive personality makes him unreliable, as he is prone to resistance to commands, and tends to dawdle in his execution of those commands. Such ideas of incorporating emotions into AI have been explored in real life, and it has been concluded that “If emotions such as anxiety, fear, and stress are incorporated into intelligent systems which deal with complex, critical tasks…the result could be disastrous”[2]. This makes Marvin less reliable.

The Heart of Gold is powered by the Infinite Improbability Drive, which by its nature has random effects. Because of the this, it is extremely unreliable. At one point, it turns the crew into yarn, while in another scene, into furniture. This unpredictability makes it the definition of unreliable. In fact, a rider can't even rely on going to right destination location!