Your friend is correct; the flu can indeed be dangerous. While similar to a cold, it can lead to severe complications, especially in vulnerable groups. The most common serious issue is pneumonia, where the flu virus itself or a secondary bacterial infection causes inflammation in the lungs. Other complications can include severe dehydration, worsening of chronic conditions like asthma or heart failure, and in rare cases, inflammation of the heart, brain, or muscle tissues. This is why proper management is crucial.