Fighting symptoms with symptoms.
We, the american people really get hooked on the outward appearance and our thoughts focus on changing that. We tend to focus on the symptom and not the problem. Often coming to grand rationalizations (entire industries) that label the symptom as the problem.
If you look into a mirror, and you see someone frowning, our immediate thought is to reach in there and put a smile on that face.
Your emotions tell you exactly how you feel about what you are manifesting in your life right now. Talking about changing, or even just accepting emotions, is counterproductive and all together silly. You do not "fix" the gas gauge to read full. You need the feedback to tell you accurately what is happening. Do not get mad at your emotions or mad at yourself for your emotions.
Thinking positive is mental training. Whether you think you can, or you think you can't, you are correct.
So much of our conditioning (media / movies) teach us to worry about everything. And again, we are working on symptoms. If you are worried about something and that gets you to think about ways to fix the problem, that is great. But, if you just worry, imagining all the things that could go wrong, then you are just sapping all your mental energy. If you can't do anything about it, you need to remove it from your thoughts.
And so, we take the true statement "You can't afford the luxury of a negative thought", and then try to change the thought, not change the thinking.