Lets say that you're married but you want to cheat on your wife. That's not good, you don't want to upset your wife and I don't want you to upset your wife. So I'm gonna do you a favour, I'll not cheat on my wife and sell you the credit! Now when you cheat on your wife it's ok, because you have a credit that negates it! Zero sum, no harm!
And you know what, I wouldn't want anyone to upset their wife so out of the goodness of my heart I will not cheat on my wife as much as I can so that I can sell the credits to other men, that way it's ok if they cheat on their wives. They don't have to worry about upsetting anyone and my good behaviour is rewarded with money!
And all I had to do was nothing, then sell the credit for it...