Many people know but they don't realize the importance of supplementing themselves of vitamins and minerals. People take for granted or are unaware that nutrient deficiencies has a big impact on their overall health. To think that eating a balanced diet is enough, is a misconception. Because, no one can really say what is YOUR balanced diet. Each person is unique and therefore nutrient requirements are also different.
Likewise, the adequate amount of vegetables needed to meet these requirements is at least 5 servings of fruits and vegetable everyday. Unless you have like a daily 5-course meal, you will not meet this requirement. So I always tell my patients to take vitamin supplementation, whether they eat more, less or adequate amount of food.