It is often said, and it is often accepted as an extremely wise maxim, that we should learn from history. That "those who cannot remember the past are condemned to repeat it." While this advice does have some general merit, I would like to advise against accepting it as an absolute. Very many people 'learn things from history', and believe that history has relayed some insight to them, when often it actually hasn't. Do they just have their facts wrong? Or are they interpreting those facts incorrectly? Neither, necessarily. My contention is that it's very possible to have a firm grasp of all relevant empirical data, as well as the arguments relating to the data, and still have a very skewed, inaccurate conception of the world and of history. So, then, where is the source of error?
The history of the world as it exists is only one of the trillions of histories that could have been. The past is, essentially, a single sample. A crucial step in the scientific method is repetition and verification (or falsification). A solid conclusion about anything is only accepted after a great many trials. We do not have the ability to replay history and see all of the trillions of possible outcomes. Had random events occurred differently, or had others besides ourselves made different decisions than they did, the results that we would see (that is 'history'), would be very different, and therefore might 'teach' different 'lessons'. Not to mention the infinite numbers of ways that seemingly unrelated events could occur differently, and thereby drastically alter all events that were contingent upon the outcome of that initial event (think butterfly effect).
Many specific lessons of history are actually reliable, simply because they have been repeated, tested and verified (or falsified) throughout the course of history. Too often, however, we believe that very recent 'lessons' of history are indicators of some overall trend, when in fact there is no reason to believe that these events aren't actually exceptions to a given rule or trend.
This is true both of history in a broad, general sense, but also true of our own personal history. If some decision that we make leads to some undesirable outcome or consequence in our lives, then we are likely to attribute those outcomes to the unwise decision. Rarely do we consider the possibility that the decision (given all information available to us at the time,) may have been a very wise decision, but that random subsequent events are responsible for the undesirable outcomes. Not to mention the fact that, in certain circumstances, any decision we make will lead to undesirable outcomes, and the decision we made may well have resulted in the least undesirable outcome, and therefore would be quite wise indeed. However, we don't get to 'see' the alternatives, so we can't ever know that this is the case. But neither should we assume that we just made a 'bad decision' (or vice versa in the case of 'good decisions' with desirable outcomes, which could have been due to good fortune). We often recognize the 'lesser of two evils' reality when choosing a political candidate to vote for, not realizing that this brutal truth extends to many areas of life. Many problems don't have 'solutions'; only trade-offs.
To further illustrate the point, let us use an example with a few, easily identified variables (where much of life has millions of difficult to isolate variables) and apply them to a mathematical decision model. Say we are considering the option of three different career paths, A, B and C. With path A we believe (given all available information to us about the prospects of the field, as well as knowledge of our own skills and abilities) there's an 80% chance of great success, 15% chance of mediocre success and a 5% chance of failure. With career option B we assign the probabilities to be 50/20/30 and with path C we determine them to be 25/25/50. Clearly, given our analysis of the available data, career path A would be the wisest choice.
So if we choose career path A and 10 years later the result is 'failure', did we make the wrong decision? That certainly isn't clear. It could be that our analysis was off, and the probabilities that we assigned were 'incorrect' i.e. not truly representative of the possible outcomes and their likelihood. Or it's entirely possible that our analysis was spot-on, and the history that we experienced just happened to fall within that 5% of the time that we knew would end in failure. However, the vast majority of people who find themselves in this, or similar, situations would immediately begin second-guessing themselves, claiming that options B or C were 'obviously' better choices. This is called a hindsight bias.
The Iraq Wars
Another example of a hindsight bias can be seen in the broader sense of history as well. Take the two wars in Iraq, for example. The first under George H. W. Bush, was swift, successful, and cost the United States very little. Opposition to this war was very small going in, and even smaller once the outcome was known. The second war in Iraq, under George W. Bush, was much longer, difficult and costly in terms of human lives (both Iraqi and American). Opposition to this war was stronger at the outset (though not significantly so) but became more consolidated once it had been under way for some time. As the 'results' were coming in they were deemed to be undesirable, or at least not worth the cost. Even though the rationale behind the two wars was not significantly different (a brutal, rogue dictator invading a sovereign nation vs. a brutal, rogue dictator remaining defiant and non compliant with weapons sanctions he had agreed to).
Many opponents of the 2nd war now hold it as axiomatic that it was a 'mistake' based largely on what they see as the undesirable results (even if they claim it isn't based on the results). Had the second war been as swift, simple and successful as the first (and the non-insurgent portion was), I find it hard to believe that opposition to the war would have been as strong as it turned out to be. Certainly there would be some people who would have opposed the war on principle, or who hold that the rationale for going into war was insufficient. But there are a great deal of others, probably a majority, who wait to see how things turn out before they form an opinion. Or who would have allowed results to change their opinion had the results been different (the results just happened to confirm their initial position in this case, at least in their mind). Many of these people aren't even actually weighing costs against benefits in their analysis, however. They are simply looking at the costs incurred and seeing that they are undesirable, not even acknowledging the fact that there would be competing costs and benefits associated with not waging war. Since these costs and benefits of the alternate reality are unseen, they simply assume that the net result there would have been preferable, without any justification for making such a conclusion. Not to mention that anyone declaring with certainty that it's either a mistake or a success at this juncture could be doing so prematurely (clearly, the long-term consequences of the war are still undetermined).
The relevant analysis should be of the conditions and circumstances, as well as the rationale in favor of undertaking the war at the time it was entered into, when the results were unknown. Divorced from what we now know, not in light of it. The decision was either wise or not on it's own merits, irrespective of the results. Because the undesirable results could have been due to innumerable subsequent decisions of how to wage the war, insufficient preparation, actions (or failed actions) of those involved, and random occurrences that occur within war that can influence the outcome. All of which are entities independent of the initial decision to wage war. Not to mention that the undesirable results could have been even more undesirable had we not invaded.
FDR and The New Deal
Yet another example of confused analysis on the basis of results is that of Franklin D. Roosevelt, the Great Depression and The New Deal. For decades intellectuals held it as axiomatic that "FDR and the New Deal ended the depression." What evidence do they submit to establish that these two events were causally linked? Simply that they both occurred at somewhat the same time. The Great Depression did in fact end, did it not?
Of course the depression ended, everything ends at some point. Markets boom and bust. The relevant question is whether or not the depression ended faster or slower than it otherwise would have without The New Deal. Scholars have more recently revisited this subject and found that relevant historical and economic data from the time reveals that it is very likely the case that FDR and The New Deal likely unnecessarily prolongued the depression. That is; had different economic, social policies been instituted, or perhaps simply had old ones been left alone, the depression still would have ended only much faster. The great depression ultimately only ended with the advent of World War II, which was much more responsible for it ending than Roosevelt's New Deal policies.
These are some very specific examples, but when you start to analyze things in these terms, you see that they are hardly exceptional or out of the ordinary. Indeed, as humans we are hard-wired to be results-oriented in our thinking, so this type of analysis is actually the default way we tend to look at things. And not without reason. Many 'results' are often distilled from hundred of years of experience, and wisdom, passed down generation to generation. Or they are inherited genetic survival traits (i.e. the man who runs from the lion passes on his genetic code, the one who stands still dies). These 'results' are often quite reliable. They have been shown to work through a de facto scientific method; trial and error over centuries. That being said, just because many of these traditions 'work', that doesn't necessarily mean that they are optimal. Not to mention that many detrimental beliefs and practices can get passed on in the form of superstition and tradition. The important thing to keep in mind is that results can be meaningful and useful when it's possible to isolate the variables responsible for creating the outcome (at least to a fairly high degree of certainty). Or when the results are repeatable and testable.
 - FDR's Folly: How Roosevelt and His New Deal Prolonged the Great Depression (Paperback)
~ Jim Powell
 - New Deal or Raw Deal?: How FDR's Economic Legacy Has Damaged America by Burton W. Folsom (Paperback - Nov. 17, 2009)