There are there three universal biological reasons prevents living tissue, and therefore human beings from repairing; these same three reasons are at the root of why anyone experiences prolonged illness:
Infection/Wind
Lack of Resources
Continued Aggravation
That's it. Only three categories, but from these three the entire pantheon of human medicine and wellness emerges.
Often times people are classified within two "extra" categories of contribution: age (too old), and genetics (born this way). However neither of these two categories present with illness that cannot be attributed to one of those three root causes.
Let's elaborate on the root factors a little further:
Infections are to modern medicine what "Wind" is to TCM. I can't cover why it's called "wind" within this article, but will eventually come back to this in future works. These external pathogens are antagonistic to our health, and if left unchecked, the responsible micro-organism will deplete us until there is nothing left to give. So our bodies will and must prioritize isolating, or becoming immune to, the infection over the less serious "aches and pains" or miscellaneous patho-physiologies.
Parasites, bacteria, fungi, and viruses are all examples of External Pathogens.
This category is ranked as priority no. 1 because external pathogens must be resolved before a wellness program can resume the more mechanical and chemical factors of healing and strengthening.
Lacking resources- many conditions originate from a lack of resource, aka a deficiency. This is where the big picture gets more complex.
Instigators of deficiency illness- Poor sleep, malnutrition, overwork, oversex, life threatening wounds.
Common examples of deficiency illness- Bloating, poor digestion, poor sex drive, dry skin, blurred vision, "heart burn," and of course Fatigue.
Aggravation- is the other side of deficiency. These are also referred to as "repletions" or "excesses." In the same way that too much sodium will increase blood pressure, too much food will increase fat, and bloating, too much alcohol will deplete your liver.
Instigators of excess illness- Over-eating, motionless lifestyle (under exercising), physical trauma, over drinking, drug usage, poison exposure, etc.
Common examples of excess illness- Muscle knots, headaches, nausea, constipation, etc.
As a rule, if you are experiencing prolonged illness, this is generally lumped into the "deficiency" category, however exceptions definitely exist. You might notice a lack of absolute correlations. For better and worse, that's what happens when your medicine is predicated off of wisdom, rather than instruments. Not every conclusion is going to be a singular correlation between one cause and one effect. However if you find yourself wondering why you are still unwell, look to the underlined red factors for your solutions (Sections 2a. and 3a. of this article).
One last note: it is important to commit to a lifestyle change before any of these three factors can begin to change for the better. It has been wisely said, "In order to heal, you must first give up what made you sick"- Someone on the internet.