Meryn Stol voted up this answer. Marguerite Leenhardt A part of the answer is the "phonological deafness". Basically, an infant can make subtle distinctions between all existing human vocal sounds pronounced around him, until the age of 8 months approximately. Then begins the "phonological deafness" that is to say your auditive system will reduce the complexity by minimizing the variety of human vocal sounds one can distinguish. That's how a infant evolves into a speaking child (put simply, of course). Given this, as a non-native speaker, your phonologic reference set may not include some of the phonemes you have to pronounce to speak in that foreign language. See question on Quora - Meryn Stol