Resistance to Taking Action on Weight Loss

Every time I think about the 15lbs I have to lose, I start to feel super discouraged. I start going down the failure thought train ‘this should be easier, I’m smarter than this, I know how to do this, I’ve done it before etc’ I end up running from the problem instead of planning and addressing. How can I change these negative thoughts when I am still feeling so negative about my lack of adequate action?