Language is a purely human and non-instinctive method of communicating ideas, emotions and desires by means of a system of voluntarily produced symbo… - Edward Sapir

Were a language ever completely "grammatical" it would be a perfect engine of conceptual expression. Unfortunately, or luckily, no language is tyrannically consistent. All grammars leak.

Getting down to brass tacks, how in the Hell are you going to explain general American n- 'I' except genetically? It's disturbing, I know, but (more) non-committal conservatism is only dodging, after all, isn't it? Great simplifications are in store for us. … It seems to me that only now that is American linguistics becoming really interesting, at least in its ethnological bearings.

Human beings do not wish to be modest; they want to be as expressive — that is, as immodest — as fear allows; fashion helps them solve that paradoxical problem.