It can be hard to ask for stuff sometimes. Maybe it's vacation time from work, borrowing some money, or asking for help moving. The times we feel hesitant to ask is because we think there's a good chance the response will be "no."
This keeps us from asking for unreasonable things, which is good. But sometimes the fear of "no" keeps us from asking valuable and ambitious questions. If you're a journalist, maybe it's requesting an interview with someone famous. Maybe it's pitching your boss on a new idea.
Rejection is always a real possibility, but you can get over it and try again. Many times you may receive an unexpected "yes" that launches your career forward, or opens new opportunities. If you don't ask, you'll always wonder what could have been. If you always ask, the worst you'll hear is an occasional "no," and you'll get over those quickly.