A miracle event (one-in-a-million) happens to a person roughly once every month.

The idea is that a person encounters events at a rate of one per second. Since people are a awake roughly $8$ hours a day, they encounter roughly $\sim 30,000$ events per day or roughly $\sim 10^6$ events per month.

This is a special case of the “The Law of Truly Large Numbers”, which says that however unlikely an event is, given a large enough sample it becomes likely.