There is an analogy between single ended amplifiers and human speech, singing production

When we speak or sing there is not one entity pushing air and another pulling it. It is just one person doing the thing! A constant flow of air originating deep inside our body is being modulated by the vocal chords which control this flow like a grid inside an electron tube or electronic valve. A constant flow of electrons in a class A amplifier is modulated by a control element be it the grid, the base, or the gate. As the signal output from the amplifier tends to 0 so does distortion tends to 0. If we overdrive after limits distortion will become serious but gradually as everything else in nature with no negative feedback. Same with an output transformer, if one exceeds its limits. Gradually.