Why do people pollute the earth even when they know it causes harm?

humans pollute the environment mainly because they dont believe that the little polluting that they do can cause a big amount of harm to the ozone layer. The fact that million or more individuals pollute the environment causes a higher percentage of damage towards the ozone layer. Up north or places that are extremely cold begin to become destroyed ,the ice melts and the cold areas become warmer causing the polar bears habitat to be gone. This is a major problem.