Take a look at the left diagram where an ischemic stroke is illustrated: It clearly shows that a lack of blood flow to the brain occurred due to narrowed arteries, which eventually forms a clot in the arteries that feed the brain. Contributing are smoking, poor diet, lack of exercise, and stress. The right diagram shows a rupture in an artery that feeds the brain blood. Ruptures commonly happen due to high blood pressure, which pushes against the walls of the artery, eventually causing it to fail and rupture. Instead of blood reaching the brain, it leaks out of the artery, failing to feed the brain the blood it needs to function.