Our thoughts participate in creating our reality all the time. Learning about manifesting is about getting conscious of that process occuring within yourself.
If you expect to be rejected, consciously or subconsciously, you are putting energy out into the world that sets that up. (Now of course there are exceptions to this and not everything that happens to you in your life is what you set up. Other people have their creations as well as their free will.)
Once when I was working with a college student who was complaining about not having any dates, I taught her the process of doing affirmations. (I like to do things at first that are more “countable” so the effect is more evident.) She came back two weeks later with a new problem: she was having so many dates, she couldn’t get her school work done. Abundance brings new issues to solve.
Getting Conscious of What You Are Creating is Important
Sometimes you can go “backwards” in your process and discover what beliefs you are holding about yourself. Look at your life circumstances. Can you tell from looking at those circumstances what you believe you “deserve” … or have been programmed to expect?