The macroeconomic ruel: SPENDING = INCOME = OUTPUT, WHICH DRIVES EMPLOYMENT is presented here in a schematic form. Output can be taken to be equivalent to  GDP. In order to maintain output it is necessary for all the income earned to be spent. If this is not the case, then companies find they have excess unsold stock on their hands and will cut back on production. This, in time, will lead to an increase in unemployment as companies need fewer employees. The shortfall in spending can be made up by any of the three sectors that contribute to total output. However, in cases where  a country has a trade deficit and where the private sector is not spending or investing enough, the only option is for the government to Net Spend i.e. to spend more than it collected in taxes causing a fiscal deficit.