Some have an illness that they have no control over and could not have prevented. Some diseases are hereditary but do have factors that contribute to them. Example: Your family history may show a tendency for diabetes, that does not mean you will get diabetes but it does mean that you should watch your diet and weight in order to help prevent it developing. Alcoholism is preventable if you do not drink. Many diseases are preventable if we are vaccinated against them. High blood pressure is a contributing factor in having a heart attack but can be kept under control with medication, so a visit to a physician for a yearly check-up is necessary. Preventive medicines such as a cholesterol lowering medication can save a life by preventing a stroke but it is necessary for us to take the step of going to a doctor and being tested. A brain tumor or something like that is not preventable. So, the answer to your question is basically....yes and no.