Hart daran zu arbeiten, besser zu werden, führt nicht immer zu linearen Fortschritten.

See, I didn't need to write in German, but you instantly understand my point better. Gleich und gleich gesellt sich gern, that's also true when it comes to speaking the same language. But you can't create born-and-raised Germans from immigrant adults, and attempting to fix them at every opportune moment just gives the impression that being better at German somehow gives you an air of superiority. In some cultures, this is just straight up bad manners, so is quoting single sentences and writing essays about them while missing the forest for the trees.