Do labor training programs improve earnings and employability, or are workers who participate in trainings usually better than others? Do private schools provide better education, or are their students more motivated than their peers in public schools? Are veterans adequately compensate for their service in the army, or could they do better in the private labor market? Identifying accurate causal relation in economics requires bright ideas, good data and a perfect empirical strategy. Modern econometrics have revolutionized economics, providing answers for important foundational problems.