If x happens and then y happens, does that mean x caused y? No. It's true that x may have caused y, but you need something more to connect them, or we'd all believe that carrying an umbrella causes rain, or that vaccines cause autism. There are plenty of other reasons those things sometimes happen together. Correlation is not causation, but it sometimes makes a good story to tell. This comic is from Zach Weinersmith at Saturday Morning Breakfast Cereal.