Why (Many) Rockets Have Fins

It’s pretty easy to memorise “centre of mass ahead of centre of pressure”, but achieving it is more complicated, especially in liquid fuelled rockets whose propellant tanks drain during flight, shifting the centre of mass as they do, and in the presence of transonic and supersonic shock waves that change the centre of pressure. This is one reason many liquid propellant rockets place the denser propellant tank at the top of stages that fly through the atmosphere.