Motivated? Challenged?

I don't know.. I really want to lose weight but then I don't last long in disciplining myself in eating the right food and eating sugary, fatty food moderately. I could easily get excited and start a diet very well but when I see myself losing weight, I also easily get contented and get back to my old eating habits. Weird huh? I know some people will get more challenged and motivated to continue their diet when they're losing but not me. I'm actually trying out some weight loss supplements now but even with this I'm not faithful in taking it.