As you know, your thoughts have energy. This energy flows within and around you, attracting whatever you're feeling to manifest your experiences.
From a spirituality perspective, you're in a constant state of creating. Positive energy brings positive experiences. So when you feel good, you energetically bring goodness into your life.
Of course, thinking positively isn't strong enough to override negative beliefs. So if you have blocks with abundance or items such as money, this may require you to transform any misaligned spiritual patterns.
Rest assured, though, when you believe, can begin to manifest almost anything you're capable of conceiving in your mind.