An increase in Gross Domestic Product can cause an increase in the quality of life enjoyed by people in a given country, but it does not necessarily do so.
GDP is simply a measure of the value of goods and services produced in a country in a given year. This is not necessarily the same thing as quality of life. The two often do go together. As a country produces more wealth, its people can typically buy more things and have a higher material standard of living. However, there are aspects of quality of life that are not material. For example, if GDP were to decline because people worked fewer hours and took more time to do things with their families, quality of life might go up. This shows that quality of life and GDP can be, but do not have to be, linked.