@Wolfie,
Not sure if LaVey was a conman or some of his friends had unrealistic expectations of him. It's hard to say because none of us was around at that time and I would take the accounts of Aquino and company with a pinch of salt.
I usually keep my promises but I remember the few times I didn't. These were trifles. Like I told my former friends I would go somewhere with them but then I called and cancelled it. Of course, there were tantrums and hissy fits. In the end I terminated all the contact with them because the relationship seemed oppressive and I wasn't feeling comfortable. Perhaps, I should have been less indecisive and set clear boundaries earlier but I was young then. It was a long time ago, during and a couple of years after studies. I think I'm more assertive now but I know from my own experience that we can sometimes say we will do something only to reconsider it later. I prefer then not to keep my word than fulfill the promise and then regret it.
Sure, if a friend at work asks me to take her shift while she will take mine another day and I say "yes", then I don't call her next day saying I won't make it. If the superior asks me to take an additional shift and I say yes, then I don't change it later. If I can't make it, then I say it immediately so that she can find someone else.
I take into account the seriousness of the situation. I'm not tribal, I'm more of a loner and I don't like it if someone doesn't show understanding if I change my mind about some trifles. I grant the liberty to reconsider to other people too. If a friend calls me saying, for example, that she can't go with me to the cinema as promised and asks not to be offended, I reassure her that it's nothing, that I can go alone and that I'm not angry with her.
Certainly, there are some crucial and serious circumstances when withdrawing the commitment can harm the person you care about but I prefer not to make rigid moral commandments for myself. Each situation is different and should be judged separately. Sometimes, it is misjudged and this is why the freedom to change one's mind seems quite important to me although I can agree that it shouldn't be used too often.