And I'll just use this opportunity to recommend David Graeber's "Debt: The First 5,000 Years" - a wonderful book about the history of economy, demonstrating how it always boils down to effective use of debt.

There are tons of great parts in it, but one that really stuck with me is his analysis of the social dynamics whereby when someone brings you a gift or otherwise does something expensive for you, you are temporarily in debt to them, and the polite expectation is that you always pay it back in a way whereby you give more than you owe, such that they will then be in debt to you (generally for approximately the same amount), and the relationship can continue oscillating, with each of you being in debt about half the time. Paying back exactly what you were given and not a penny more is thus considered to be an indication that you want to discontinue the relationship.