Eric Warmenhoven is apparently annoyed by the oft-repeated statement that "everything happens for a reason."[1] People who state this typically mean that God's plans are often not evident to human perception, and that time will show the good that will come of some event. This represents a crucial mistake.
Eric is absolutely right, the statement as it stands, is a horrid misunderstanding of cause and effect. Even if you properly take into account the concept of free will, a given event happened because of some past event. That is to say, it was caused by that past event or choice. The actual teaching is that God will bring good out of everything, even out of evil. This is only superficially the same as the preceding, erroneous, statement.
In bringing good out of evil, God is not, usually, side-stepping causality (though He can). Joan of Arc's preservation of France was not miraculous (well, perhaps it was, but it was not miraculous in the sense that it happened after the need for it). Rather, all that is necessary is to realize that from her choices and actions, God inspired certainly, but still rooted in causality, we later came to a situation where Catholic France would not be brought down when England betrayed the Faith in the Protestant Reformation. Again, the two statements, even with this example, remain very very similar. Someone in between St. Joan and the Reformation would know the reason for France's freedom: St. Joan acted. They would not however know the purpose for her actions. Specifically, they could guess her purposes for acting, but not God's for inspiring and aiding her actions. It is the purpose that will come clear with time, the purpose for which God did allow it, or the purpose for which He will use it, or both. It will be used as a cause, and the things it will cause remain unknown.
In some sense, this really is the same as saying the reason is unknown, but only if you think, as Calvin taught, that everything is predestined. It is not. You did not get sick because you needed to suffer. Adam did not sin because Jesus would save us. Rather, Jesus saved us because Adam sinned. Adam is the reason, or cause, of Jesus' coming, Jesus is not the reason, or cause, of Adam's sin. Now everything is as clear as mud. ☺
[1] http://www.warmenhoven.org/blog/7