Francis Shaeffer gives some insight into the evangelistic encounter in his The God Who is There.

"It is impossible for any non-Christian individual or group to be consistent to their system in logic or in practice. Thus, when you face twentieth-century man, whether he is brilliant or an ordinary man of the street, a man of the university or the docks, you are facing a man in tension; and it is this tension which works on your behalf as you speak to him. A man may try to bury his tension and you may have to help him find it, but somewhere there is a point of inconsistency.

Every person is somewhere along the line between the real world and the logical conclusion of his or her non-Christian presuppositions. Every person has the pull of two consistencies, the pull towards the real world and the pull towards the logic of his system. He may let the pendulum swing back and forth between them, but he cannot live in both places at once." (p.133)