What would be the hardest thing(or hard things) to live in a different country??

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I am originally from Japan and I have been living in USA for almost 10 years.I had a hard time associating with people who couldn't understand how hard it is to live in country where is different from your home country. I couldn't understand English well when I came to Ohio state where I lived at the first.I was 19 and I tried my best to understand what people says but lots of people laughed at me and also made this face that "you are so stupid that you cannot even understand what I said in English!". I have grown up in totally different culture,language,life style this and that but I tried to fits in the best I could and most of poeple who I have met there was very cold and mean. Many people looked at me with strange eyes and some people even told me that I better go back to my country because I cannot speak English well and I am also an asian so I am an outside after all. I became stronger than before but It is still my bitter memories. What would be the hardest(or at least hard things that you could imagine)to live in a different country than where you have grown up??