I have a lot of trouble forgiving people for being flaky. It feels, to me, like people flake on me more than they do on others. If I make a social plan, I assume there’s a 50% chance it will get canceled on the day of. Much of this is probably a by-product of being 23 year old recent college without a strong social web, but it’s still true of long-time friends and even ones that live nearby.
I have ADHD, and am far from being perfect in this regard. I am often late, but I go to extraordinary lengths to never cancel plans. As a response to my general disorganization, my parents hammered it into me that being late or canceling indicates a lack of care and consideration. I haven’t observed this to be true in my own behavior, but I really don’t ever forgive myself for flaking. When I fail to show up for someone else I REALLY beat myself up. But…I also don’t forgive others who flake on me. So I don’t often initiate plans, knowing there’s a good chance I will be extremely upset with them afterwards.