What is the single most important variable that determines a country's economic prosperity and standard of living?

So often it is said that many variables determine a country's economic growth and prosperity such as being a democracy or a dictatorship, high birth rate, high death rate, low birth, low death rate, natural resources, no natural resources, education, geography, institutions, immigration and emigration, culture religion, diversity and homogeneity, human capital, brain drain, state capacity, state competency, good governance, corruption, stability, state of war, state of peace, trade, no trade globalization, no globalization, capitalism, socialism and so on. But what if there is really only one single variable that determines these other variables. After all many of these other variables are connected to one another, for instance, state capacity and good governance are closely connected and often go hand in hand. So what is this one variable?<br> <br>Many tend to argue that it is institutions that matter the most for example Acemoglu and Robinson in Why Nations Fail. They say that good inclusive institutions such as good property rights, rule of law, and an impartial judiciary as well as political institutions like free and fair elections are key to prosperity. However others argue that it is state capacity that matters more than institutions and that state capacity and good governance are far more important than democratic institutions for example Iraq has good democratic institutions but bad governance. Some also argue that it is human capital that matters most and that better education and healthcare are more important for growth than good institutions. Others argue that geography, state capacity, religion and culture play a much more important role. So what is the single most important variable that determines a country's prosperity?