It is normal for us to tell the truth. Our minds want us to tell the truth and we show stress when we are lying. When we lie, whether on purpose or subconsciously, our bodies produce physical signs. This is how trained professionals are able to tell if we are lying or not and is the basis of how lie detectors work ;)

Of course! . . . No, I mean... maybe not. Sometimes.

If you mean "Do you think the first answer that comes to mind is correct?" It depends on the context. If it's a question concerning an area in which I'm highly competent, my first answer is usually correct. If you mean "Do you think the first answer that (spontaneously) comes out of your mouth is the truth?" Well, at least I can say it's true for me. (Unless I'm being robbed, and I'm telling the robber I have no money.) ;)

Thanks for your answers . they are all logical on me. The answer comes to our mind is from our subconsciously and sometimes we don't believe that and try to think more and more then we answer the wrong :) in the other hand , in sometimes it doesn't come to mind any responses. I think the thing is depens on the topic!