Wrong, it is never perfect and that is the point. A pixel that exists conceptually as a discrete rectangular area within your framebuffer is mapped to a diffuse point on a screen by an analogue system that is highly susceptible to electric and magnetic fields. Everything about it, from it's position, shape, brightness and even it's colour are affected by multiple, nonlinear effects. You will never get the same combination of these effects from one day to the next. Your CRT display literally is never the same twice.
And that is why our US television standard was superior for so many years over the European ones. You guys with your PAL system that never does what you really want it to. Here in the US we used NTSC (Never The Same Color). Our analog interference was a FEATURE!
