Why are viruses not considered truly alive?

The answer

Viruses lack the machinery for metabolism, energy production, or reproduction on their own. They are essentially genetic material (DNA or RNA) wrapped in a protein coat. To replicate, a virus must hijack a living cell's molecular machinery, reprogramming it to produce copies of the virus. They don't eat, breathe, grow, or respond to stimuli independently. This places them in a gray zone - they evolve through natural selection like living things but are inert particles outside a host.