M.O.B is an acronym made famous by rapper Tupac Shakur which stands for "Money over Bitches." M.O.B is best thought of as being a philosophy which denotes that a man who wants true power must always put money first and women second.
A similar philosophy was also espoused by the fictional gangster "Tony Montana," played by actor Al Pacino in the movie Scar Face, in which he said that in this country(the USA), first you get the money, then the power, and then the women.
From an evolutionary biological perspective, men will compete for females, and females will compete for resources, that is, men that can provide them with security.
Men who choose to chase women first, before they have cemented their wealth and status, waste precious time and energy, because even if they are successful in finding a female in this state, this female will in all likelihood trade up to a better man if she meets a man who is wealthier than her current man, and will leave him.
Men of low status who manage to acquire attractive females through charm and wit are at risk of losing these females when faced with a male of higher status that has more resources and or charm and wit. By focusing on resources, aka money, first, a man increases the likelihood that not only can he attract the most beautiful females, but keep them and pass down his genes.
My buddy asked me if I thought his girl was cheating on him. In response, I asked him the following questions.
Do you have a job?
He responds by saying "no."
Do you live at home with your parents?
He responds by saying "yes."
Do you spend a lot of time with her?
He says "no."
Does she have an ex boyfriend who has more money than you?
He says "yes."
My final conclusion to my friend was that, more than likely, she is cheating on him, and to avoid having this happen in the future, he must follow M.O.B.