Thinking about Great Expectation

I don’t understand what is the meaning of great expectation. It was hope and dream. I am not sure. I had a dream when I was eighteen years old. I hope I can work in ICAC that look like a police. I had great expectation in one year ago. I can study in United States that was a good chance for me. There has high quality of education, and I can learn a good English. It can let me easy to go to ICAC. I thought I seem like Pip. He wanted to be a gentleman, and I wanted to be a law enforcement officials.