I came across this yesterday, that explains this 'knowing' that so many have an issue with:

"religious faith is not like scientific knowledge.
We are, of course, familiar with non-scientific ways of knowing. If we love someone we would never dream of trying to prove it scientifically. In fact, when we love someone we surrender the need to be all-knowing and to control. We live with the mystery of the other person.
Religious faith has more in common with knowing someone we love than with scientific knowledge.
There can be a temptation to treat religious faith like scientific knowledge, but this will only lead to a dead end.
In fact, it becomes the ultimate betrayal of faith because we no longer trust God, but think we can do it all on our own."

[Fr Gerard Kelly]