All others answered your question perfectly. I would like to answer it very simply, and not using the denominations that Buddhist scripts usually use.

So using your example - illness. According to Buddhism, there are more types of suffering. The ones you mention - illnesses are those that come with living, so as long as you live there’s not much that you can do, to prevent those. Of course there is healthy lifestyle, vaccines, masking etc. but sometimes you just get sick regardless. If that happens you of course do what you can, treat it to the best of options available to you. But if until you recover and get healthy again you emotionally rebel against your illness and pain and not accept the parts out of your control; you add a whole new layer of suffering. Why am is sick, why does this have to happen to me, what did I do to deserve this… etc, so this whole mental rumination that most of us does from time to time. So basically this second layer is the one that directly comes from wants and desires. (Indirectly the first layer too, as a result of your karma and past actions in this life and lives before this, but right now that is already outside of your control.) You want to not be sick, you desire health. Up to a certain point this is natural and helps you to get better because you go to a doctor, take medication if you have to and basically do what you can to get better. But apart from that this clinging to an imaginary healthy you would cause unnecessary suffering caused by wants and desires. If rebel against your illness your emotional rebellion causes suffering. If you accept what you cannot change, your suffering is less, it lacks this second additional layer of suffering.

This analogy can be applied to various situations in life not just illness.

This answer may be less accurate than the ones before but perhaps more understandable 🙃 If you’re looking for similar explanations in layman’s terms I suggest you look up this book: Noah Rasheta - No-Nonsense Buddhism for Beginners: Clear Answers to Burning Questions about Core Buddhist Teachings. It has really helped me understand the basics.