Humans more fit to fear dangerous situations survived more, therefore as a survival mechanism we've learned to have fears. This infographic shows what happens in our brains when we have fears and what people's most common fears are.
How to close a sale? A great list of under-utilized common sense. I think sometimes certain tactics are too obvious to be trusted, and we sales folk go the long way because the short road is suspiciously short. They are called fundamentals for a reason.