Traditional chemotherapy is toxic to all cells. Cancer cells grow rapidly (part of what makes them dangerous). So the toxic effect gets the cancer cells first, since cells that are growing take up the most chemotherapy. But other cells grow rapidly too, like hair and intestinal cells, which is why cancer patients lose their hair and have terrible nausea/diarrhea.

All (almost all?) cells take up some chemo. So, you are actually dying, just hopefully more slowly than the cancer. And then we stop the chemo before you all the way die.

This is why the bar for a cancer diagnosis is so high. We need biopsies to try to get as close to 100% accurate diagnosis as possible.