Systems thinking is the 5th discipline, that brings 4 associated disciplines into a cohesive tool allowing people in an organization to perform at a level higher than the collective talent within that organization. In systems speak, this principle is called emergence. As an example, if you look at hydrogen and oxygen separately, you will see 2 gasses. When combined, the emergent characteristic is wetness because they combine to create water.
When systems thinking is applied correctly, the organization transforms from knowing to become a learning organization. The 4 disciplines that support systems thinking are Personal Mastery, Shared Vision, Mental models and Team learning. Through a cycle of self-development, people enrol in the organizations vision and become committed to its success rather than being compliant.
Commitment results from an alignment of personal goals with the organizational goals, enrolling in the vision rather than buying into it. Committed people make the difference and are prepared to discuss problems openly and effectively by entering into open dialogue and leaving all assumptions at the door in order to resolve them.