Picking a fly fishing rod is a tricky endeavor. Do you go with your ego, expected fishing environment or something else? While length is a factor, the bend or action of the rod is a key factor.FlexibilityFly fishing rods are often defined by their flexibility. In laymens terms, flexibility means how far the rods will bend when the same casting effort is used.Minimal BendA fly fishing rod that has minimum bend is often called a fast rod.