Take a chance on me?

How many chances do you give people? Maybe it depends on who the person is? Is it a friend? love interest? The President?
I understand that people come into your life and may leave without you ever knowing why. I am glad for many people that have "come for a visit", shall we say. Whether it has been a short visit, or one that has meandered through parallel experiences along my journey.
I'm still slightly in touch, via facebook, with my very first best friend. Over the years we had fought like cats, and after moving away, we would write letters, see each other in the summer, and somehow, we drifted apart...Until facebook. Now I can check in to, at least ,see how she is doing, even if I might not do it daily, or weekly...I can find her again and check in(as I do with most people).
I'm not sure why or how we lost touch, and maybe it doesn't matter. There are people that I still think about who were in my life for practically just a moment, that have touched me with kindness, or not kindness, and I often wonder what happened to them...
There are others, who have been more recently involved in my world, who I thought would be around forever, and are not. No, they haven't died, just not involved in my world anymore. I know what some of my actions that may have caused these absences, but maybe not all of it was my fault, and some people, I might not ever know what happened.
There are people that are coming back into my life that I didn't think would EVER come back, and I would have bet BIG money that I WOULDN'T LET it happen. You know the saying, fool me once shame on you, fool me twice shame on me...( I think that the rest of it should say fool me three times I'm getting a gun).
And yet, here I am giving someone who may or may not be deserving of my time and attention another chance at friendship. Because I believe that people DO deserve another chance. I believe that people CAN change. I've changed.
I sometimes think of it this way. When someone goes to jail, serves their time for whatever crime they committed, they are released back into society. They are supposed to get the benefit of the doubt and get a new chance. Hopefully, they have learned the lesson of what not to do, made amends and won't do it again. Now, I'm not saying that I've ever gone to jail. But I have been ostracized from a group of people that I thought were my friends, or family, for actions that I take full responsibility for my part in.  Maybe, I'm not going to get a chance, and maybe I'm not ready to give them a chance. That's just the way that it goes sometimes. But knowing that pain of isolation from people who were supposed to be your friends, your support system? Well, it makes you rethink how you treat others who want another chance. Of course with MAJOR walls of protection around you(Good luck breaking these puppies down).
But how do you determine which people get that chance? 
Recently, as you may or may not know, I was supposed to go on a first date with a guy that I haven't met yet. O.K., so final plans were never really in concrete. He said he was going to call to define what we were going to do... Call didn't come,  I made other plans. No big deal, I don't know this guy from Adam. He attempts again, I'll make it up to you, I was an ass for forgetting...OK. I'll give you another chance, against MY better judgement, only because a friend of mine said something at work that made me think, well we didn't have a definite anything set, just that we were supposed to meet on this day.
SO, I agreed, but I want to know what we are doing and when. I want a definite plan made. We made plans for dinner at 6pm that Wednesday. After I got done from work I was supposed to meet him at a Thai restaurant close to where I work. Wednesday 4pm~ I get a text from him saying that he wasn't sure that he could make it and that he would call me if  he could. By the way, it wasn't a family emergency, he was acquiring a vehicle all of a sudden...4pm? ON the day of? Seriously? OK( I wish you could hear this Ohhhkaaaayyyy the way my former supervisor in Cleveland would say it). Didn't hear from him until a week later. Asking for forgiveness, in email,  because it was bad timing... This was his 3rd offense in making, albeit somewhat vague, but plans, and breaking them, followed by silence. I'm sensing a pattern that I don't think I need to be involved in. Not sure if he will get another chance even though he "really wants to meet me". Yeah, it totally seems that way dude. Good luck with that. (You do know that I LOVE sarcasm right?)
Yet, at the same time I'm giving a friend whom has literally threatened me with violence, another chance, because I hope this time that she really has changed,. But mostly, because I believe that she wants to make amends. Because I know when she is good, she is very, very good...but when she is bad...she's horrid. =o)

There are two other people that I keep giving chances over and over again to as well. Both have hurt me immensely. I mean deep, cavernous wounds that start to heal and then get deeper when they hurt me again.
With the one person, I swear each time that I won't let them hurt me again. I won't expect ANYTHING from them so they can't let me down. Because I feel, that if you expect something from someone who continually disappoints you, you will always be disappointed. But if you don't expect anything that they say they will do, and they actually do it, they surprise you pleasantly.
Of course, you might "prefer" if they actually did some of the things that they say they'd do, or even pleasantly surprise you more often, but hey, a girl can dream right?
But then, the person who I continually give more chances to than ANYONE, is myself. I have done the MOST damage to myself. I used to avoid getting into fights with tough girls who wanted to kick my butt by showing them that they didn't have to, I could do it myself. I would run around in a circle literally bending my leg behind myself to physically kick my own ass. This was supposed to be my way of diffusing the tension, making a joke. It worked, many times.Thank God I've got long legs! But inside, I was doing more damage than any of my former bullies ever knew or could. But that's a different story for a different day. Another chance for me to honestly write about whatever may come up.
So how do you decide whom you give chances to?