Why Did I Do This?

I just confessed to my parents that I ate all the cookies meant for my sister's birthday party. It was so stupid! Now she'll be mad at me, and I'm already feeling guilty before anything happens. Okay, wait, let's rewind. Why did I do it? The cookie jar is always there when I want a quick snack. Maybe it’s because they're right by the kitchen where I spend most of my time now that we’re all working from home? Or was it just because they looked so good and my sister wouldn't notice if one or two were missing? Anyway, why do people feel better about eating something when they think no one is around to see them eat it? Does anyone else have this issue too? How can I explain myself to her now that the truth is out? Any advice on how to make it right would be really appreciated. What should I say?