I believe my biggest fear was that I would just overall hate it. It's hard to commit to 4 months of anything intensive (think: committing to going to the gym 7 days a week, only the language version of it), especially flying away to a country as culturally different as China.
There were many different misleading and useful pieces of advice I had heard about going to China, but what I learned is that every person has such a nuanced experience in this country that it's hard to put a pinpoint on it.
At times I would say to myself "Ah, I know what this person meant now," but other people's perspectives varied in positivity and would sometimes paint a picture of what I expected my experience to be like. I try to keep a balance between cynicism and optimism, but kept an open mind and went in knowing that I would have to form my own opinions.