If we only got sugar from easily recognizable sources the problem might be less encompassing. However, sugar comes in so many different forms it is not easy to determine how much sugar we are consuming. Foods such as cereals, breads, pastas, rices, crackers are all quickly converted to simple sugars as soon as we eat them. Even dairy products like milk, cheese and yogurt are quickly converted to simple sugars soon after we eat them.
When we think we are eating a healthy breakfast of cereal with milk and a piece of toast we are actually getting a hefty dose of simple sugars. This is why we are either hungry or sleepy within a few hours of eating a breakfast like this.