On our paths to self-discovery, we make goals, set milestones and keep track of our progress. It's a continual calibration, as simply setting a goal isn't enough. Forward movement requires making choices that support our goals.
You and you alone have to choose what you will be loyal too. We know all too well how easy it is to get distracted, and to go back to an old habit "just this once". We each have to decide what is truly important to us, and sometimes, we have to face rough truths. That piece of chocolate cake may seem like it's just what you need in the moment, but is it truly more important than a goal of cutting back on sweets? The answer is "Yes" if you do end up giving in to the cake.
However, you also discovered a weakness, which you now can consciously take steps to address. Help yourself out! If you stay up too late at night looking at your phone, stop complaining about how little sleep you get. Make the conscious decision to leave your phone in another room at night. If the phone is right by your bed, you'll be tempted to look at it. Build up your inner strength and determination so that you can keep your phone next to you without giving in to looking at it.
What is essential throughout any journey towards accomplishing a goal is DO NOT GIVE UP! If you eat that chocolate cake, own up to what you did, and then recalibrate your actions to be inline with your goals. Also take a moment to truly reflect on how that deviation made you feel? Did the cake address the desire you felt before you ate it? Did it live up to the hype? Did you end up in a sugar-induced stupor? Perhaps you want to cut back on video games or watching TV - give yourself a chance to really find out what it feels like, don't assume that you will always want to keep on doing the same exact things you are doing now.
Keep getting back to your goals, no matter how far off track you might feel. Keep your mind open to new and creative ways to accomplish what you want as you progress through this beautiful life we've been given.