Why do you need to breathe faster at the top of a tall mountain?

It is not true that you need to breathe faster at the top of a tall mountain. In fact, the opposite is true. At higher altitudes, the air is thinner and contains less oxygen. This means that your lungs have to work harder to extract the same amount of oxygen from the air, and so your breathing rate slows down. However, your heart rate will increase to compensate for the reduced oxygen levels.