General Usage:
* The company's success is underpinned by its strong customer service. (Meaning: Strong customer service is the foundation for the company's success.)
* A solid education system is the underpinning of a prosperous society. (Meaning: A good education system is essential for a prosperous society.)
* Trust is the underpinning of any healthy relationship. (Meaning: Trust is the foundation of a good relationship.)
More Specific Examples:
* The scientific evidence underpinning the theory is compelling. (Meaning: The theory is supported by strong scientific evidence.)
* The artist's work is underpinned by a deep understanding of human emotion. (Meaning: The artist's work is based on a deep understanding of human emotion.)
* The economic reforms were underpinned by a belief in free markets. (Meaning: The belief in free markets was the basis for the economic reforms.)
Figurative Usage:
* The ancient walls, now crumbling, still underpin the city's identity. (Meaning: The ancient walls are a symbol of the city's history, even though they are no longer in good condition.)
* Her confidence was underpinned by a quiet strength. (Meaning: She had an inner strength that gave her confidence.)
As you can see, "underpinning" can be used in various ways to convey the idea of support, foundation, or underlying principle.