You see, the weakest part of a spinning reel is the main shaft that supports the spool. If the pressure is too great and the rotor arm does not flex, the main shaft can very well bend, turning the reel into Quasimodo; the Hunchback of Notre Dame. Yes, high-end monster fighting reels have rotor arms that are stiff and will not flex. That is because they’ve got a freaking fat, rigid, and tough main shaft that is built to take very heavy pressure. For cheaper reels, the answer lies in the balance between the flex of the rotor arm and the main shaft.