On the Comment trail, Frances suggests that this whole question revolves around whether or not one is religious: If there is a God, then things happen for a reason; if not, then there is no overseeing power, and the answer is that everything is random.
I'm not sure that the question is as simple as the existence of "God," however, as monotheism accompanied by omniscience and omnipotence is only one option. Even the Old Testament Jehovah seems to be rather less than omniscient--he's always discovering, invariably to his displeasure, that something has happened without his awareness.
The Romans, for example, were often quite religious, but they were polytheistic, and recognized the idea of foreign gods they had never met. Sometimes it was a matter of 'my god can beat up your god,' and they were quick to adopt new gods and bring them on home. And the Greeks, of course, had a reasonably consistent pantheon, but interacting in an ongoing soap opera--and one god was often doing something while another was distracted.
Even so, it's not at all clear that the Romans or Greeks believed that everything happened because one god or another willed it. Their gods didn't necessarily pay much attention, nor did they seem to have a "plan" for humankind. They became intensely involved in the affairs of certain groups or certain individuals at certain times, but that's quite different from any sort of masterplan.
The idea that "God" is responsible for every detail of every thing that happens, with individual angels plucking leaves from trees at some predetermined moment, is very much a medieval Christian theory. Many Buddhists are quite religious but manage to get by quite well without a detailed plan from God; and, in Thailand, where the dominant religion is Buddhism well-supplied by Hinduism and whatever other pantheistic beliefs happen to appeal, there is a belief that prayer and sacrifice can influence events, but that doesn't mean that god(s) determine everything that happens. Sometimes they get involved, sometimes they don't.
Thailand is also a hotbed of astrology, and astrology presetns some interesting questions. Astrology doesn't always assume a god or gods. Nor do all forms of astrology assume the predetermination of events, despite the emphasis on timing. Some forms of astrology claim that certain 'flavors' of events will happen at certain times--for example, that one will go through a creative spurt, or will be physically challenged--but they attribute this to something more like the underlying laws of the universe, for which the movement of the planets is a sort of large clock.
In the view of some astrologers, we are on boats floating down a great river. The cosmic clock is able to tell us the sorts of things we will encounter as we float down the river--at this time there will be turbulence, further on the river will widen and smooth out--without attributing agency and purpose.
As to the people who RDJ meets in Los Angeles who say that everything happens for a reason--well, I suspect that most of them are vaguely New-Age California types, who would describe themselves as 'spiritual but not religious,' and don't believe in god or gods in the traditional sense, but have some sort of belief in a big soft fuzzy benevolence on the part of something out there somewhere.
Me, I believe in the Norse Gods and the Frost Giants. Ragnarok is Coming!