Reasons require a Reasoner. Rules require a rule-giver.

While it is likely that some people mean this statement metaphorically (as we do when we speak of "natural laws" even though they aren't literally laws in the sense of "given by a law-maker" ) I am not comfortable using this saying. For me at least it leads to expectations of order and comprehensibility in my life, that I am in no way entitled to.

Sometimes things happen for no particular reason. Life is just a series of things happening, and we don't have the perspective often to even see the whole causal chain, much less grasp it.

There is no inherent wisdom or plan so we shouldn't be talking about the "reason" for this or that in some overarching sense.

My wife, who is not in any way a believer, nevertheless uses this term or its opposite, "it wasn't meant to be", to sort of let go of her expectations and move on down the road in the face of disappointment. While the phrasing is technically "off", I see what she's doing there, and I don't hector her about it. I just don't use those words myself. For me it's more, "Whatever, just more disappointing shit. I believe I shall lower my future expectations even further into the toilet". One can argue that her circumlocution is more mentally healthy, even if less accurate, I suppose.

Everything does happen for a reason, but we might not know what that reason is. The universe is well-ordered.

This is the best of all possible worlds.