My biggest fear is that bitcoin will completely fail to live up to Satoshi's vision, bitcoin was not created to gain value, buy $1 today & get $3 tomorrow, that's not it. We can see that people are now pegging the value of bitcoin to FIAT, not bitcoin itself. So i just fear that people are forgetting what bitcoin was actually created for & its intended purpose. In addition, another fear is that central parties will monopolize bitcoin one day.