Your mitochondria are susceptible to defects and damage for various reasons. Mitochondria are structurally unique because they were once a type of bacteria that invaded the cell. But through the course of evolution and time, mitochondria have made a permanent home in our cells. Unlike nuclear DNA, often seen in the shape of an ‘x’, mitochondrial DNA is always in the shape of a ring. While this allows the DNA to be transcribed easily, it also makes it vulnerable to damage.
Chronic stress, disease, certain prescribed drugs, and opiates interfere with NAD+ metabolism, thus short circuiting the energy production of cells. This is like Superman trying to fly with kryptonite in his pocket.