Promises
As the philosopher William Godwin explained, promises are irrational. Suppose I make a promise to do X, and then it comes time to keep it. Now, according to my best judgment doing X is either morally right or wrong. If I judge X to be right, I would do it anyway, so my promise is superfluous. If I consider X wrong, then I have promised to do wrong and to violate my own judgment. Therefore, promises are either redundant with, or contradictory to, my judgment of morality.
Promises involve predicting the future. I predict that my promise will be reasonable to do and will be possible to do. The person I promise to predicts he will want it in the future. I predict nothing will come up that will dramatically change the situation and make me strongly wish to not fulfill the promise. Can all these predictions be made accurately?
My predictions may be pretty good, but I am fallible and they are not guarantees. Unfortunately, a promise is "a declaration or assurance that one will do a particular thing or that guarantees that a particular thing will happen". If I can't guarantee my predictions about the future are accurate, then how can my promise provide any guarantee? Fallibility prevents absolute guarantees, and promises are all about offering them.
An example of an irrational promise is to love someone, and live with them, forever. You can't predict the future that well. What if the person becomes a murderer? Then you'll have to break your promise. If you will break your promise under a variety of unspecified circumstances, why make it at all? Sometimes people make promises to fool themselves: they can't have a guarantee, but they want to pretend they can.
Promises and trusts should not be accepted, either. Trusting a person is setting up a situation where I might become a victim. If the trust is broken, I lose out, and it's his responsibility. I'm creating a situation where bad things may happen to me, but I will say it's not my fault and there's nothing I could have done about it. It's better to run my life (as much as possible) so I have control over my own success or failure, and if anything goes wrong it's in my power to think of and implement an improvement.
Trusting someone consists of refusing to take responsibility for my own judgement and expectations about the person. This saying sums it up: "Fool me once, shame on you. Fool me twice, shame on me." The point is we can't have perfect knowledge and may sometimes get burned by a person once, but if it happens more than once we should have known better and not trusted him, and not put ourself in a situation to rely on him. If he explains why the first incident was unusual and persuades you to rely on him again, fine, feel free to, but if he lets you down, it was your mistake to judge him reliable and not take sufficient precautions.
Trusting people in such a way that if they don't do what you expected, you will blame them for a broken trust and be upset with them, is setting up your life to have fights.