@maco in that case I should have never been able to learn the English th sound, or the English l in kill, or the Japanese l/r sound. Yes, there are sounds that are difficult to master and some are probably impossible, also depending on genetics (my sister can’t do the Spanish rrrr with her tongue at all), but to say it’s impossible to learn new phonemes as an adult doesn’t seem right to me at all. Where does this come from?