What causes faith and doubt?

I very much doubt I can answer this question but do have a few ideas about it. I am 45 years old and can say I have never had much faith in others or religions. That isn't to say I don't trust people, I do trust and usually give it to easily. Why do people have faith in something they have no real proof of other then what they create from within themselves. They will deny what others have done for them just to give credit to what they have faith in. I was reading a blog and it was about how people think praying and having faith makes the special. It was actually asking why would their god answer their pray while denying that same answer to others. Did they think they were special and the ones denied were less faithful? Faith has probably done more harm then good.

Everyone has doubt in all things. The amount varies but without doubt we would still be stuck in the stone age. Think about it and you might get it. I will expand on this in another post.