Why was the NASA's probe Mars Climate Orbiter destroyed?

The Mars Climate Orbiter was robotic space probe launched by NASA on December 11, 1998, to study the Martian climate, Martian atmosphere, and surface changes.

Its missions was to study the Martian weather, climate, and water and carbon dioxide budget, in order to understand the reservoirs, behavior, and atmospheric role of volatiles and to search for evidence of long-term and episodic climate changes.

It was destroyed when a navigation error caused it to miss its target altitude at Mars by 50 mi (80km), instead entering the martian atmosphere at an altitude of 35 mi (57 km) during the orbit insertion maneuver.

The navigation team at the Jet Propulsion Laboratory (JPL) used the metric system of millimeters and meters in its calculations, while Lockheed Martin Astronautics in Denver, Colorado, which designed and built it, provided crucial acceleration data in the English system of inches, feet, and pounds. JPL engineers did not take into consideration that the units had been converted, i.e., the acceleration readings measured in English units of pound-seconds^2 for a metric measure of force called newton-seconds^2. In a sense,it was lost in translation.

Still, NASA does not place the responsibility on Lockheed for the mission loss; instead, various officials at NASA have stated that NASA itself was at fault for failing to make the appropriate checks and tests that would have caught the discrepancy.