One thing you should understand is that human desire and quest to make money is endless and as such they will continue to fail there promise because of wanting more and more. You wouldn't blame your friend though, because I myself has made a lot of unfulfilled promise. People get overly excited and make silly promise and failed after making such promise. so in such case I see it as normal. but in some case it reduces a person personality because your words or promise may not be much valuable or respected by your friends.
Just like d saying that human needs ate insatiable and so they don't stop wanting more and aswell never get to the point where they get completely satisfied and want no more., the needs keeps growing by the day, they more they get, they mire they want. Promises are something that form some persons they consider it their word which by extension is them giving part of themselves and so whenever they make a promise they try to keep to it because it's their word and for some others it's just a cliché and so they don't consider it as any serious but with time they get to understand the importance of such and so much blames shouldn't be thrown at your friend actually because it may be different with him.