You can fix things that reproduce during your lifetime,” said Godde. “The cells that get damaged, you can fix that. But the body walks a tightrope. It only has so much time and resources to fix things. So, our body is not a perfectionist. It’s as if it’s saying, ‘Oh, well, that’s pretty close.’ Plus, there are parts of our body that have cells that aren’t going to divide and grow again. For example, our nerves and our brain cells are kind of a one-shot deal.”