When you bend only the butt section, you are using the strongest part of the rod and applying a lot of pressure. But as the tip rises, the bend moves up the rod until you are fighting the fish with the fragile tip. That is why you are breaking rods. When you use 10-pound-test tippets or stronger, you need to fight and lift heavy or strong fish with the butt, never with the tip. Obviously, fragile tippets will mean using more of the tip section to strike and fight a fish.