Anyone who has ever tried to explain the English language to a non-native speaker knows what a frustrating experience it can be. The grammar is confusing, there are a ton of irregular verbs, the spelling makes no sense and the pronunciation is a nightmare.
BUT, at least, even if your pronunciation isn't perfect, you can still be understood fairly well. The sheer volume of accents present in English attests to that.
Vietnamese is not like that. Very vowel and consonant has to come out exactly right or the words is different or unintelligible. It's terribly frustrating, though rewarding in its own way.