I've learned through heartbreak and remake that one chance should be enough. No one deserves a second chance. I've come to this conclusion because people shouldn't need to prove themselves to anyone more than once.
From both perspectives I've seen it all. I have been guilty of allowing myself to become vulnerable to people more than once and that has come back to burn me. When someone genuinely wants to be a part of your life they should never be asking for a second chance and they shouldn't be causing you any heartache or distress.
Someone who is going to be there for you will only need one chance to prove that they will be there in the long run and won't ever prove otherwise. From the perspective of someone who has also been guilty of being the one to ask for more than one chance to be in someone else's life, I have come to the realization that I don't deserve this specific person in my life and I have not been someone that they can count on. I have hurt not only this person but also many more by letting them down and then asking for forgiveness.
I believe that asking for forgiveness and another chance is what the norm currently is. This also seems to be the route that people want to take instead of being people that can be reliable. You should be proving to those who matter that they are important to you the first time and continuously be showing them that you care.