That occurs because employers know that when wages decrease, workers will shirk and expend less effort. Employers avoid shirking by preventing wages from decreasing so low that workers give up and become unproductive. The higher wages perpetuate unemployment, but the threat of unemployment reduces shirking. Before current levels of world trade were developed, unemployment was shown to reduce inflation, following the Phillips curve, or to decelerate inflation, following the NAIRU/natural rate of unemployment theory since it is relatively easy to seek a new job without losing a current job. When more jobs are available for fewer workers (lower unemployment), that may allow workers to find the jobs that better fit their tastes, talents and needs. As in the Marxian theory of unemployment, special interests may also benefit. Some employers may expect that employees with no fear of losing their jobs will not work as hard or will demand increased wages and benefit. According to that theory, unemployment may promote general labour productivity and profitability by increasing employers rationale for their monopsony-like power (and profits).Optimal unemployment has also been defended as an environmental tool to brake the constantly-accelerated growth of the GDP to maintain levels that are sustainable in the context of resource constraints and environmental impacts. However, the tool of denying jobs to willing workers seems a blunt instrument for conserving resources and the environment. It reduces the consumption of the unemployed across the board and only in the short term.
Unemployment, according to the OECD (Organisation for Economic Co-operation and Development), is people above a specified age (usually 15)  not being in paid employment or self-employment but currently available for work during the reference period.Unemployment is measured by the unemployment rate, which is the number of people who are unemployed as a percentage of the labour force (the total number of people employed added to those unemployed).Unemployment can have many sources, such as the following:

new technologies and inventions
the status of the economy, which can be influenced by a recession
competition caused by globalization and international trade
policies of the government
regulation and marketUnemployment and the status of the economy can be influenced by a country through, for example, fiscal policy. Furthermore, the monetary authority of a country, such as the central bank, can influence the availability and cost for money through its monetary policy. In addition to theories of unemployment, a few categorisations of unemployment are used for more precisely modelling the effects of unemployment within the economic system. Some of the main types of unemployment include structural unemployment, frictional unemployment, cyclical unemployment, involuntary unemployment and classical unemployment. Structural unemployment focuses on foundational problems in the economy and inefficiencies inherent in labor markets, including a mismatch between the supply and demand of laborers with necessary skill sets. Structural arguments emphasize causes and solutions related to disruptive technologies and globalization.