I think the most painful realisation comes when you find that you cannot speak your mother tongue as well as you do the language of the land where you grew up. My English is evidence of this. When something as simple as a colour, or the name of an animal in your mother tongue leaves you dumb. Yesterday I could not find the world for ‘turtle’ in Somali, only after my mother reminded me, did I recall knowing it.
We betray our mother tongues, for the languages of nations who will never fully accept us. We let the strangeness infest our mouths until we forget how to accommodate our original tongues.