Floating shelves look fragile to the naked eye because of the way they sit on the wall. All the workings of the brackets are hidden so it seems as though they are floating there on the wall. In reality they are usually much stronger than other types of shelves which are supported with traditional brackets and screws.
Have you ever tried to install a set of shelves only to find that the brackets get in the way? No matter how you change it around, you just cant seem to get it right. There is a type of shelving that can help you avoid this problem altogether, they are called floating shelves.