Also not very hard. Sometimes I wonder if our mouths are more elastic than American people's.
Our brains learn only to distinguish sounds we have learnt as a child (or with a conscious effort later in our lives) and it's pretty normal not being able to reliably hear sounds that are not present in any language you know.
For example I'm from Poland and I learn Romanian and when I tell my family, they can't hear the difference between Romanian "apa" and "apă" (which are two different words) at all. They hear them as the same word. In Polish we don't have "ă" sound (which is schwa in English) so whenever a Polish person without much foreign language knowledge hears "ă", his/her brain will match this sound with the closest sound they know, which will be in most cases "a", sometimes "e" (I mean Polish "a" and "e", in English these letters are pronounced with various sounds in various words). Polish has relatively few vowels but we have a lot consonants and consonant clusters that are unpronouncable for Western Europeans without a lot of training for the same reason.
I'm talking not only from my experience, I've also seen once on TV an experiment when people had heard a recording and were asked how many different sounds they could distinguish and English speakers could only hear 2, while Spanish speakers 3, because one of the sounds was the one that is present in Spanish language but not in English language (I can't tell which one because i couldn't hear that one myself too

).