One of the things my dad would tell us kids when we complained that one of our siblings got to do something we didn't, or when we saw other kids having fun that we weren't allowed to have was "Life's not fair." I was reintroduced to this concept when studying the lives of the early apostles, namely Peter and James. Both were very close to Jesus, as they along with John comprised the three apostles who Jesus brought with Him to the transfiguration. However, they met different fates. Peter was imprisoned with John by the Sanhedrin as recorded in Acts 5, but then angels delivered him by night. Peter was imprisoned by Herod Agrippa, and again angels delivered him by night. Acts 12 then states that James, on the other hand, was imprisoned by Herod Agrippa and beheaded.
Why so different? Why does Peter get delivered two times, yet James gets martyred? Wasn't Peter the one denying Jesus, cursing at the very thought that he and Jesus were friends? (Mk 14:71) And wasn't James the one that did the opposite, desiring to call down fire to judge a city that didn't give Jesus his due? (Lk 9:51-56) Yet Peter gets spared, and James doesn't.
There's no reason why. Life's not fair, because God's ways are higher than our ways. (Is 55:9) As the clay, we have no grounds to complain to our Potter that we're not made into the form we desire. (Is 45:9) It's tough to know that we're not in control, because we like to think we know better than God, when we know that's not really the case - even when we're given decisions to make, we still mess things up and do things we wish we hadn't done. We can, however, take heart in knowing that God is infinitely wise, kind beyond measure, and loves those who love Him (Pr 8:17); therefore we can willingly cast all our cares about "fairness" on Him, because He cares for us. (I Pt 5:7) Though we can't understand right now why He allows things to happen as they do, He's promised to work everything out for good (Rm 8:28) and I believe it.