finding out

According to the General Social Survey, 20% of married men and 13% of married women reported having sex with someone other than their spouse.

In the United States, 17% of all divorces cited adultery on the part of either or both parties.

But 70% of married women and 54% of married men reported they didn't know of their spouses’ extramarital affair until their spouse confessed.

And how did the other 30%-46% figure it out?