A bruise will heal quicker if there is sufficient vitamin C in the body. And an individual will recover more assuredly from an illness if the immune system is working as it should, which requires adequate nutritional reserves as well. In addition, there are sometimes obstacles that must be removed before healing can take place. For example, a foreign object must sometimes be removed before a cut can completely heal. The body has the capability of healing itself.
Germs are the cause of disease.
Heredity is more important than environment.