Do we know any event (or whatever else) which has no reason?
Reasons (causes) are constructions of human mind. There are many things that human mind has not been able to explain with reasons.
I like the following example my friend told me.
Imagine a man walking down the street that gets hit by a flowerpot falling down from a balcony above.
You may ask: what is the reason for the flowerpot to begin falling down from the balcony?
I can say: the wind has suddenly increased in intensity and it has puffed it off (taken it down) from its unsecured place.
You think a little and then you ask: what is the reason for wind to puff off the flowerpot? I can say: there is no reason. Wind is notorious for being really hard to predict and it always behaves differently. It is not predictable. The reason stops right here.
(Of course, with enough data about the state of environment and massive computational capacity, it is possible to make predictions of future movements of air, so there is some additional reason. But the prediction is always inaccurate, so the reason is always imperfect and what is worse, such predictions gets less accurate with time. Quantitative weather forecasting gets the more unreliable the farther into future the prediction is made.)