That question is only legitimate if you believe that God exists and that He is the creator of all things.  For those who believe, I have a profound personal experience to share, one that many parents will be able to relate to:

When our youngest daughter Michelle was about 3 years old, she needed to have her tonsils taken out.  My wife was with her at the hospital as much as possible during the day, while I arrived there after work.  Michelle was very uncomfortable but seemingly not in much pain because of the medication she was given.  When the attending nurse wanted to give her an injection to calm her down, Michelle strongly objected, by waving her off.  I told the nurse that she should not give Michelle the medication and that I would hold her to keep her calm.  I held her all night and she slept most of the time, resting peacefully in my arms.

Michelle obviously did not know why she had to go through this harrowing experience, but at the time she trusted her parents that we loved her, and this love helped her during the night.  As parents, we often need to do hurtful things for our children, things they don’t understand and that they would much rather not go through.  However, as long as they are young, they believe and trust the parents enough to unquestioningly accept what needs to be done.

God is that faithful and loving parent and we are the children who are unable to understand why God allows hardship and evil to happen.  But, as believers, we know that God uses all things, ALL things, whether pleasant or hard, for our good, to conform us more into the image of His dear Son (Rom 8:28-30).  While we may not understand the reason for suffering; at least for believers, we know that good will come out of it.  And as for unbelievers, we need to leave this up to God, for who knows; God may be using that same calamity to bring salvation.