Shipud writes: Smokers who quit often gain weight. This has usually been attributed to decreased metabolism, and/or food replacing smoking as a reward system. New research shows that changes in gut bacteria may explain weight gain in those who quit smoking. The changes in the gut bacteria in people who quit smoking are startling. Moreover, the type of bacteria that emerge in the gut after smoking cessation are the same type that have been shown to cause obesity.
Computers are unreliable, but humans are even more unreliable.
Any system which depends on human reliability is unreliable.