Original: Modern returning boomerangs can be of various shapes or sizes as can be seen in the diagram of modern Boomerangs to the right of page.
Simplified: However, some boomerangs do not return because their wings do not have the right profile. Most of the boomerangs are made for right-handed use, left-handed people have to use other boomerangs that are mirror-inverted or have to throw with their right hand.