The reason most catalytic converters fail is due to fuel that doesn't get burnt by the engine in the combustion process.
The fuel that doesn't get burnt by the engine then gets into the catalytic converter and causes the catalytic converter to heat up which destroys the components and metal inside the catalytic converter.
Catalytic converters contain several high priced and precious metals which degrade when it's heated up and then it causes it to clog once the metals fall apart and lodge into the wrong places.
Engine misfires due to bad spark plugs, spark plug wires and and bad ignition coils or low fuel pressure can all cause engine misfires.
Failed engine components, warped engine heads, worn piston rings, faulty valve seals etc are all causes of a catalytic converter to fail.