@jonathaneze perfectly possible if you just add one more aspect into the argument. Let's say B is renting a piece of land from A to start a business, and the previous agreement is that B will repay once they break even.
A: I need you to pay me back right now
B: That's not possible, paying back right now means it will take longer to break even and gain a profit, so it'll just delay the next payment
A: That is not my problem, you have not paid me the fees for this month yet, and you need to
B: I told you again that i cannot, why don't you follow our previous agreement? I will pay you once i make money
A: And then what if you don't? Your business has barely any customers in the last month, how can i be assured that you will break even in any time at all?
B: That matters not, you have signed the agreement, and you do your part, and i'll do mine
And then it repeats