Why Did I Eat All The Candy?

So last week, I found this huge bag of candy that my sister had hidden in the back of our closet. At first, I just took a couple pieces because it was only fair since she'd been hoarding them from everyone else. But then...I kind of lost control and ended up eating almost all of it myself over the course of two days. Now I feel terrible about breaking my diet plan but also can't help feeling oddly satisfied at having outsmarted her candy stash. What does that even say about me? Is there something wrong with being a bit competitive or is this just a weird coping mechanism for stress?