Emotions are a weakness.

The Cyberman became the embodiment of detached, heartless, emotionless logic - except for they times they flounced about, shouting and waving their fists, or stood around in spaceship corridors seemingly nattering about the weather.

As the Fifth Doctor noted, the Cybermen were unable to appreciate the small, beautiful things in life: a flower, a sunset or a well-prepared meal.

The Cybermen were the inhabitants of the planet Mondas. Originally twinned with Earth, Mondas drifted off into to the far reaches of space, only to return in 1986 with its energy supply completely tapped out. In The Tenth Planet, the Mondasians decided they would recharge their doomed world using Earth’s power - until they got their sums wrong and blew up Mondas through an overload.