Fighters who mainly just throw left hooks constantly. Joe Frazier type of fighters. Left hookers are hunting opportunities to land left hook flush. Whenever you throw left hand or right hand they are always trying to counter it with left hook. Can this style make you do well in boxing, what about in amateur ring? How you'd fight against left hooker fighter?
Expect it coming, weave under the left hook, right hook to the body on the way through. Pivot, left hook to the body, right hook to the head. Being predictable is NOT a good way to fight.
Frazier is one of my favorites, but success with that style requires levels of focus, fitness and toughness that most people are unable or unwilling to attain...not to mention that the hook needs to be a special one.