You have to make or find the reason. It isn't just there.

explain definition of happenstance and offer that no one has solved the puzzle of anticipating the result of 3 random objects in space and their relation ship to each other after one second

You do that and you'll end up hurting someone without meaning to. Faith is something that's impressed upon us right from childhood and most of us forget to question it. It is the last resort for them to fall back on when nothing works out or something unexpected happens.
You take that away and it creates an all consuming void. I'd rather you ease them into reality of space and time. Be patient.

In my line of work--psychotherapy--it is actually a professional ethics violation to seek to "convert" any patient from one belief system to another. I have to be very cognizent of that. I have totally lost count of the number of patients who came in totally distraught at some tragedy or other, only to struggle even more with the dubious mission of wringing some sense of reason or divine plan out of horrible suffering. Some get very angry at "God" and others decide they must have done something to deserve this "lesson." They can get really down on themselves, insisting on searchimg for meaning out of suffering and destruction. One thing I have done with Christian patients is to point them to the book of Job as a lesson in the futility of trying to decifer a logical plan from chaotic or destructive events. There is a Biblical passage that says humans will never understand the mind of God. I use that as a basis to suggest that if there is a divine plan, there is no reason to expect events to make any sense to us, no matter how much we want to believe. That leads to the idea that trying to keep some sort of cosmic score card of "fairness" just leads to frustration, disappointment and resentment. Better to focus on recognizing the good stuff in life to be appreciative of, and to file the pain and suffering bits away under "shit happens." ***Of course what I WANT TO tell them is that Job is an example of just how petty and caprecious the Judeo Christian God character is and therefore bogus.

If you believe in determinism, then everything does have a reason, just not a purpose; everything has a cause.