Aging
Aging has been a particularly annoying issue for the human race for thousands of years since it ensures that no matter how healthy we keep ourselves, we all pass away at some point. Most individuals are unaware that there is now no known biological or scientific explanation for why we age. In actuality, it is totally possible to halt the harm that aging causes to live cells. In one study, scientists were able to repair mice's vision by undoing the DNA damage that builds up with age, effectively bringing the cells back to a younger, more functional condition.
This indicates that, despite the fact that we still don't fully understand why aging occurs, we do have a decent knowledge of what aging does to the body. One example is that as we age, the stem cells are programmed to create fewer and fewer red blood cells; however, it is unclear whether this is because the cells are preprogrammed to do so from birth or if our environment plays a role in this process. The mitochondria, the cell's powerhouse, also plays an unexplained role in death because it ages all of us and becomes damaged and less effective over time, though the exact reason for this remains unknown.