Hobbes argued forcefully in Leviathan that in a state of nature, human life would be "poor, nasty, brutish, and short." He says that left to their own devices, individual people are driven by fear, and this fear impels them to fight fiercely and selfishly for themselves alone and to crave power over others. Since there are no laws in a state of nature, people will murder, hurt, and steal from each other to survive. And because individual human nature is innately animalistic, people will always descend to their basest instincts if left on their own to survive.
However, while a state of nature makes life a misery for individual humans, the fear of this leads to a good outcome. People, driven by the need for self-preservation, decide to bind together into communal society. To be saved from their own worst instincts, humans have invented monarchial and parliamentary systems, in which a strong leader or a strong group of leaders imposes peace and order on the state. Hobbes calls this the social contract: under it, individuals attain to a better and more secure life by relinquishing some of their freedom. They have to obey laws they might not always like and curtail their own desires, but so does the rest of society. This way, almost everyone prospers in a situation far better than that offered by a state of nature.