There you are, thinking: "you will pay for this!"
While still in the planning stage, of course you would want the others to suffer as much as you did, or worse. Most of the time, you think of doing the same thing to them. It is a natural mechanism that would make them feel what it's like to be in the situation. Another is by initializing a different evil plot far worse than what was done to you. This is often planned together with pride, as you would want others to go down on the ground. Well, figuratively.
During the actual event itself, you anticipate the initial reaction or response of the target. It is also the time when you savor the moment and rejoice for the feeling that you have finally avenged yourself. As the tension fades, you start to notice that there is something lurking in the depths of your heart. It's a certain sensation sent to your brain that makes it wonder if you're doing the right thing. Are you getting the point here? Meaning, there is an emotional side effect on you. Your conscience won't let you get away with what you've done.
After the entire scenario, there you are, feeling so bad. You're having this intellectual battle against your mind, your conscience haunting you forever. Then you start to think positive and just let the so-called "golden rule" be the one to straighten things out. If I am not mistaken, it goes something like: "Don't do to others what you don't want them to do to you".
Revenge is sweet. But it gets bitter. Revenge feels good. But it's bad. How ironic.