Yeah, I've experienced this quite a bit. even with people keeping in touch.I had a cousin who promised to call at a certain time, but never did.then when I'd call her to see what's up,instead of talking, she's set a new time,the phone never rang with her call. I've also had that with others. And sometimes THEY actually get annoyed with YOU when you bring it up. My mother has a "friend"{?}who was a beautician, promises to give her a haircut, the day comes and goes, she postpones it, that day comes and goes.I think these people have no intention of doing what they say, but figure they're "pacifying" you by "yesing" you. But it's an insult to your intelligence,because they think you won't figure out they lied to you.Is it a sin,well, if it's a lie, yes.Jesus said,let your yes mean yes, and your no, no.