After hundreds of years of advances, medicine is good at fixing simple problems-- cuts, bone breaks, infections, some diseases-- but unreliable in the long run.
Most of its cures, both for nagging and life-threatening problems, are temporary fixes. Medicine can give temporary relief for colds, sinus, respiratory and digestive problems; but not keeping these from coming back again. There are pharmaceuticals for almost everything, which work some of the time (enough to pass a statistical significance test), but full of side-effects, drug interactions, and dosage issues. Once you start treatment for a condition, there is rarely an end to it. Everyone's personal medical history is a series of readjustments that may or may not work, to varying degrees and lengths of time.
Medicine is not an advanced science by the standards of physics, mathematics, chemistry, and engineering. Principles of physics hold almost without exception--- (i.e. specifying the environment in which they work, for instance on the earth; leaving aside conceptually outlying areas like the beginning and end of the universe.) Math is reliable, precise, and capable of dealing with high dimensions of complexity. Engineering is good at constructing machines that work reliably over a long period of time (like turning on or off a light switch); when they break down, it is easily traceable to defects in materials.
There is nothing in medicine equivalent to turning on a light switch or the ignition of your car. Medicine is moderately effective in alleviating ailments once they happen. But: it can't stop them from happening in the first place. It can't stop them from happening again. It can't stop the cascade of one problem after another. Undergoing multiple procedures, operations and hospitalizations are a sign of impending death. Advanced medicine is good at keeping you alive when you are sick, until it isn't.
Even in the midst of life, medicine is poor at predicting when something bad will start. Why you get cancer in the first place, and why at that particular age. Most serious problems come out of the blue. They may have low probability, but the statistical distribution covers up ignorance over why they happen when.
No wonder many people still hold beliefs about God's mysterious plan, destiny, bad luck, call it what you will. Saints continue to be recognized in the scientific age, mostly on the basis of a medical miracle-- attested by a medical doctor who stated that the patient was in hopeless condition before they called on the aid of a holy person. Such events are not surprising, given the iffy record of medical prognosis.
In its defense, medicine is playing in a harder field than physics and engineering. Those deal with closed systems, where strong causal procsses are set up to operate without interference from the environment. Experiments in physics and chemistry were designed to isolate a specific process in a laboratory situation where the rest of the world is excluded. Engineering creates machines shielded from anything extraneous getting into its engine, its plumbing or wiring. Medicine deals with living bodies open to the external environment: germs and viruses (with their evolutionary pattern of parasitism); physical stresses, collisions, falls, aging body parts; social, psychological and emotional stresses, all coursing through the brain, nerves, muscles, tissues and organs. It adds up to multiple causes, most of them weak in themselves, impinging from an unpredictable external environment, and interacting in complicated ways inside the body's internal environment.
And the body itself is far from being a linear causal sequence like electric lighting or an automobile engine. Instead, it is like an orchestra of string instruments, harmonizing well when opposite processes balance each other out, and subject to far-reaching effects once it gets out of balance.
All of which suggests future medicine can keep on making incremental advances. But it is implausible that it will ever make people healthy forever (or past age 100, whichever comes first); or head off when serious illnesses will start within the life span.
