Everything happens for a reason. Either it is the reason of physics, which inexorably requires that all events absolutely follow one after another according to known laws... or it is that all things take place because of the inscrutable expression of the Will of God, which is transcendent and beyond man's understanding.
Although the former does not presuppose or require the latter, the latter definitely allows for the former, and, furthermore, explains that the former is both a consequence and requirement of the latter.
We have, once again, Ibn Arabi's exquisitely developed Islamic metaphysics to support this; and if we want to turn to Buddhism to understand their conception of the transcendent, perhaps nothing could be better than the flower ornament Sutra. The concepts are equally sophisticated and inextricably linked to one another, since they both express aspects of the same truth. The fact that human beings are unable to understand what the reasons behind things are does not eliminate the reasons. Even eliminating God does not eliminate physics and chemistry; nor does it eliminate philosophy, since even philosophy, like physics, functions with or without gods to guide it. Hence, there are reasons.
Perhaps the question ought to be, what is the reason that there are reasons? And this is the question that one ignores, if one walks right past God on the way to the machine shop.
Let's move on to the second aspect of the question: why is it irritating to hear people glibly say, everything happens for a reason?
In a supremely reflexive action, I will now point out that the last essay, plus the above, underscore how enormously complex and interesting this idea, things happening for a reason, is. Having people toss it off as a given is very nearly dismissive of the important questions it raises. Moreover, the off-the-cuff expression of this, as though it did not need to be examined, or was itself an explanation of some kind, is annoying simply because it does not pay the very question it frames with sufficient respect.
In essence, when we make statements of this kind, we make them not mindfully, but mindlessly. Habitually. That is to say, they are pasted over situations like a Band-Aid in order to somehow justify them, instead of confronting the terribly difficult and challenging truths they represent. They are meant to offer some kind of comfort; but the comfort is bogus. In fact, as we have just seen, the idea provides anything but comfort, if examined carefully.
The careful examination of ideas leads us to discover that the things we assume to be true are, in fact, questionable; in trying to discern reasons, the limits of our knowledge are tested and found wanting. We are confronted, in the end, with a mystery; and to glibly dismiss it without examination is to miss the content and the message. If things happen for a reason, and the reason is a Divine one (as most of those who say this imply) it is our task not to just dismiss this and move on, but to make an inner effort to actively discern reasons — reasons which may, in the end, leave us profoundly uncomfortable with who we are, what we are doing, and why things are the way they are. The thinking-and-searching individual is irritated with pat answers; they seem to be insufficient.
The insufficiency comes from a failure to examine one's inner state, one's conscience, and the conditions of consequences and life, and take the lessons that these impart regarding the need for our submission to God. There is, in other words, a demand for serious and active contemplation built into everything happens for a reason; and yet we wave one hand in the air as though it takes care of the matter, allowing us to move on to more important things, like which team will win on Sunday.
In summary, perhaps it's lack of mindfulness itself that renders statements like this both inadequate and annoying. Mindfulness demands a constant sense of the Presence of God. It's true, Grace provides a sense of that Presence within its own action, a sense, furthermore, that transcends any ability we have to invoke it.
Yet Grace cannot be treated as a given; if we just sit there waiting for it to come, why do we deserve any such privilege in the first place? No, an active stance in relationship to the higher is necessary.
And perhaps the problem is that "everything happens for a reason" is, in the end, a passive attitude. Instead of calling us to a search, it seems to excuse us from one.
May your soul be filled with light.