"Why does humanity feel an innate need to pay a debt?"

This is a question that a friend of mine, who is in Bolivia for the year, asked in a blog post that I just read. He asked this question after walking through a Cochabamba market where people were buying and giving sacrifices to Pachamama (mother earth). Thinking about it, at home, people have a tendency to try and never be in debt to one another, because they don't want to owe people anything. Perhaps this comes with the independence so valued in Western culture, but at the same time, is it something that could be applied to all cultures?

How do you reconcile a feeling of indebtedness to God since we will never not be indebted to Him? Should you even want to?