Suffering, good people and Holy Quran

I am still discovering the Quran, thus my question might look stupid. From the Quran's perspective, why *good people* often *suffer* from awful *diseases* which are often *not related* to their *lifestyle* (ex: cancer)? Do pain and suffering among these *good people* is something covered somewhere in the Quran? Is there a reason to that since it could like some sort of *injustice*? Thank you.