This quote, by writer Nora Roberts, is based upon the principle of “nothing ventured, nothing gained”. It is a reminder to take risks and go after what you want in order to achieve it.
If you don’t ask for something, the answer will always be no. If you don’t take a step forward, you will remain in the same place.
Therefore, if you don’t go after what you want, it is likely that you will never have it.