Stanislaw Lem - Ananke (from "More Tales of Pirx the Pilot")
Such was the brain, so overburdened with spurious tasks as to be rendered incapable of dealing with real ones, that stood at the helm of a hundred-thousand-tonner. Each of Cornelius’s computers was afflicted with the “anankastic syndrome”: a compulsion to repeat, to complicate simple tasks; a formality of gestures, a pattern of ritualized behavior. They simulated not the anxiety, of course, but its systemic reactions. Paradoxically, the fact that they were new, advanced models, equipped with a greater memory, facilitated their undoing: they could continue to function, even with their circuits overloaded.
Still, something in the Agathodaemon’s zenith must have precipitated the end—the approach of a strong head wind, perhaps, calling for instantaneous reactions, with the computer mired in its own avalanche, lacking any overriding function. It had ceased to be a real-time computer; it could no longer model real events; it could only founder in a sea of illusions… When it found itself confronted by a huge mass, a planetary shield, its program refused to let it abort the procedure, which, at the same time, it could no longer continue. So it interpreted the planet as a meteorite on a collision course, this being the last gate, the only possibility acceptable to the program. Since it couldn’t communicate that to the cockpit—it wasn’t a reasoning human being, after all—it went on computing, calculating to the bitter end: a collision meant a 100 percent chance of annihilation, an escape maneuver, a 90-95 percent chance, so it chose the latter: emergency thrust!