Read the manual.

Pain can be efficient or counterproductive depending on the individual. The threat or pain is usually more efficient than the pain itself. Your "let's be pal" approach is not far from the KUBARK's recommendations, but it is not incompatible with coercitive methods: On the contrary several of these consist in putting the interrogatee in a state where the interrogator is perceived as a reassuring presence.

Context about the kubark manual on Wikipedia