Just because two things correlate with each other does not necessarily mean that one is causing the other. For example, there is a high correlation between children's shoe size and their maths ability but this does not mean that having bigger feet makes you better at maths (or vice versa). High correlations are sometimes cause by a 'confounding factor' which affects both variables. In this example, age is the confounding factor because it affects both shoe size and maths ability (because as we get older, our feet grow and our maths ability develops through schooling).