Jevons paradox
In economics, Jevons paradox is a paradox about resource usage. It is also called Jevons effect, after William Stanley Jevons who first observed it in 1865. Jevons observed that the steam engine James Watt had developed was much more efficient that the earlier model  of Thomas Newcomen. Despite this, the use of coal in England increased. The improvements James Watt had introduced made coal a cheap source of energy. As a consequence, Watt's steam engine was more popular, and its use was more widespread. So even though each steam engine used less coal, the demand for coal increased, as there were more steam engines.