To fix a problem, do you need to know what causes it?
In a word, no.
In complex systems, such as human bodies, eco-systems, societies – it might be very difficult to pinpoint ‘the cause’. This is because many things often can be changed to in turn change the effect, and similarly, many things interact with other things in various feedback loops, such that it is often difficult or impossible to disentangle cause-and-effect in any simple, point-of-contact way.
For example, if someone has a health problem, you can attempt to pinpoint exactly what mechanism is ‘misfiring’, such as to cause the symptom. This is often more simple from the patient’s perspective, if it can be achieved. Another way to do it is to apply very broad ‘rules of thumb’, things that are in general good for a person and very well may cure the problem (in addition to other possible health benefits).
If someone came to me for health advice, and if upon consideration I were unable to delineate a simple cause-and-effect solution, I would recommend very general things that tend to put people into better health – consistently good sleeps, certain kinds of exercise, getting outside, good amounts of sunlight, certain things to eat and not eat, decreasing stress, and so on.
In some cases, these suggestions could ‘fix the problem’. In a sense, if they do then one knows ‘what caused it’, but in another sense one does not.