Every once in a while, I get in a blue funk for which the book of Ecclesiastes in the Bible is a good antidote. This might seem strange, since it is by no means a cheerful book. Consider, for example, Ecclesiastes 2:9-11:
So I was great, and increased more than all that were before me in Jerusalem: also my wisdom remained with me. And whatsoever mine eyes desired I kept not from them, I withheld not my heart from any joy; for my heart rejoiced in all my labour: and this was my portion of all my labour. Then I looked on all the works that my hands had wrought, and on the labour that I had laboured to do: and, behold, all was vanity and vexation of spirit, and there was no profit under the sun.
But the blue mood I referred to has less to do with any real suffering -- compared with a great many, probably the great majority both in history and today, I have no really valid complaints -- and more to do with the suspicion that I have stupidly lost opportunities that could have made me truly happy. If only I had had the nerve to ask this girl out, or if my courtship of that other girl had been successful; if only I had chosen a different major in college, or had chosen a different career path after getting my degrees; if only I had taken a different job within my current career path; if only! Then I would surely feel less vexation of spirit. King Solomon answers me, "Don't worry about that, kid. I had all the women, all the wealth, all the power, all the success, all the acclaim -- all the things that men strive for -- and it all turned to ashes in my mouth."
This life is, as the Salve Regina reminds us, the Valley of Tears, neither Eden nor Heaven, and these worldly goals cannot change that. It's not that different choices and outcomes are without consequence -- they do matter somewhat -- but they are not the One Thing Needful.
This year, it is easy to see people making the same mistake on a larger scale -- but hardly for the first time. For ages Europeans have lamented, "If only the Roman Empire had not fallen!" Over the years, this has been echoed in such cries as, "If only the Arabs had been crushed when they first burst out!" "If only the Crusader states had lasted!" "If only Constantinople had not fallen!" As we come closer to the present age, the laments become more controversial. "If only Europeans had not discovered the Americas!" "If only the Spanish Armada had succeeded!" "If only James II had remained in power!" "If only the French Revolution had not taken place!" Closer to home: "If only Stonewall Jackson had not doubled back and been shot by his own men!" "If only Lincoln had survived to the end of his term!" "If only America had joined the League of Nations!" And, of course, "If only Kennedy had not been assassinated, Camelot would have lasted, and JFK would have ushered America and the world into a utopia of peace and justice and love and joy and wisdom!" Feel free to add your own; we all do.
Each of these examples were important to history. Each of them caused at least some people to suffer. Some of them, like the Kennedy assassination, were sudden and unforeseen, and could have been avoided by trivial circumstances; others, like the fall of Constantinople or the Crusader states, were long foreseen and could not have easily been prevented. The point remains that whatever good may have come from changing these events would be a good subject to decay.
For example, there is a trope in science fiction about going back in time and killing Adolf Hitler before he came to power. "If only he could have been removed from history, how much suffering could have been avoided!" Maybe, but we will never know. Hitler scarcely invented antisemitism, nor did he create the dissatisfaction with the end of the First World War, so the Nazi Party would still have come into existence, maybe under the leadership of Hermann Göring. The alternative leader might have been more cautious, proceeding more slowly than Hitler did -- slowly enough, perhaps, to avoid alarming the public in the USA and UK, slowly enough to allow Germany and Italy to properly prepare for war, slowly enough for Germany to develop ballistic missiles (like the V-2 rocket) and jet fighters before the war even began, maybe even slowly enough for Germany to develop the atomic bomb. What happened in real history was bad enough, but it could have been even worse.
Like Tantalus, we are tormented by seeming goods that we cannot actually attain. Maybe this is part of our punishment; at any rate, it seems to be part of being human. In the final analysis, though, all we really need to mourn are our sins, and we must remember that
all things work together for good to them that love God, to them who are the called according to his purpose.
EDIT: Reading this again, I see I switched back and forth between two different ideas. The first is that worldly success is not enough to make us truly happy, even while we have it; the second is that worldly success is both incomplete and transient. Ecclesiastes also makes the same two points, and although they are different (like the soul and the body) I think they are related (like the soul and the body).
EDIT 2: Perhaps it really is "part of being human", since even Jesus engaged in it. "O Jerusalem, Jerusalem, thou that killest the prophets, and stonest them which are sent unto thee, how often would I have gathered thy children together, even as a hen gathereth her chickens under her wings, and ye would not!" -- Matthew 23:37
EDIT 3: Don't misunderstand my previous edit. OF COURSE Jesus understands history better than we do, and He properly values historical events. Jerusalem allowing God to gather her children together would not have been merely worldly, and it is PRECISELY what was needed to make them truly happy. He does perfectly what we do poorly; but regretting what might have been still seems to be part of being human.