We&#x27;re constantly bombarded with radiation by simply living. We wouldn&#x27;t make it to adult hood if all DNA damage was lethal. DNA damage is more likely to be repairable or outright kill a cell than cause cancer, just by pure numbers.<p>&gt; Chemotherapy is just &quot;let&#x27;s kill enough percentage of this guys cells to kill the cancer cells before they kill him.&quot;<p>That&#x27;s exactly what I said with &quot;otherwise indiscriminate treatments.&quot; Our body is not a homogenous mass of one type of cell; different cells react differently. If cancer cells react disproportionately negatively to a substance than other cell types, then that substance could be useful to treat cancer. All forms of hormesis are basically an extension of this idea: that the harm done by a substance can be otherwise offset by positive effects.