Fairly New With a Long Road

I am fairly new to MFP. I have a very long road ahead of me. I am trying to lose 125 pounds. I have a lot of people telling me that I cannot do it. I am hearing things from you would look stupid that thin, to you could never lose that much weight. I would be lying if I said it does not bother me at all because it does slightly. However, I do want to accomplish this and I want to make them eat their words. Mostly, I need to do this because my body does not need to be carrying the extra weight.