What are some must-read books for people in their 20s?

Well, as a young adult, reading is an important key in developing your intellectual ability to comprehend and deal with life, but that alone won't be of important value if you don't have people skills. By this I mean, you should go out and interact with other individuals and get to know about they experiences in life and learn how to deal with the hardships that come with the day to day activities. You can get so much knowledge in books, but it won't be of help if you can't share it with the outside world.

Well instead of reading books people in theirs should go out and travel, learn.