Four Cornered Triangle

Plot: Our protagonist is an impenitent observer. Having adopted as principle, watching almost everyone and everything and learning every detail, he works at a tobacco warehouse. Even though everyone calls him “Observer,” he is actually a watch guard. In fact, he observes and also uses his observations. But he loses his grip. Because, those who talk about their observations and easily utilise them are not favoured at all. Does a rectangle has three corners or does it have three corners just because one sees three corners while standing at the other corner? Can a rectangle be three-cornered as well?