We tend to eat more if we see fat people?

Most people will say we get fat because we eat too much and exercise too little. A surplus of energy = fat gain. If calories-in out number calories-out, we get fatter. This makes sense, because back in 1900something a German dude by the name of Carl von Noorden proclaimed that we get fat because we take in more calories than we expend. He was applying the first law of Thermodynamics to the human body.