This happened some 25 years ago.

My housemate had a few of his friends around and two of them announced they were going to get married. I kept pushing questions like "If you don't intend to have children, what's the point?"

Well, about a week later the housemate returned from a night out and said that the girl had told him, and I may be implicated in this, that she thought she was getting married to the wrong guy. The two of them started a relationship, which continued for a year or so.

The guy later told me that, at the time, he was angry about my putting pointed questions to him, very inappropriate, but later thought they were good questions was actually quite grateful that I had put a spanner in the works before the marriage took place.

I felt quite proud for having done that, and if I see a couple about to get married, I won't let social niceties stop me from asking "why?" If they can't stand up to that, they can't stand up to the inevitable problems which will arise during any marriage.