All the things we use or consume are obtained from resources on the earth. The only thing we get from outside is energy which we receive from the Sun. Our resources are not unlimited. With the human population increasing at a tremendous rate due to improvement in health care, the demand for all resources is increasing at an exponential rate. The management of natural resources requires a long term perspective so that these will last for the generations to come and will not merely be exploited to the hilt for short term gains.
Another factor to be considered while we exploit these natural resources is the damage we cause to the environment while these resources are either extracted or used. For eg: mining. Hence sustainable natural resource management demands that we plan for the safe disposal of these wastes too.