Casual remarks or promises that may seem unimportant to you may strike a chord with the other person. You’re then expected to come up with the goods. If you fail to do so, your worth as a true person is in doubt–and it becomes hard to alter that judgement. […] The client would use such behaviour as a barometer of trustworthiness.
A poor memory can destroy relationships. But it’s an interest problem, so it can be cured. Simply take more interest in whatever is important to the other person. You must make the effort to pick up people’s reactions to what you are saying or doing, in any kind of relationship.
More often than not, the other party will not convey their real feelings about your sins of omission […]. Your forgetfulness or thoughtlessness is quite likely to result in a rift. You can lose a friend or you can lose business. And you may not even know why.
James Borg – Persuasion