That's pretty much what I think IM. It's really easy to let your mind go slack and find all sorts of justifications for how it's ok to just give up. I think for me the important thing is to be conscious of these thoughts and control them instead of letting them control me.
Besides, I'm still losing weight, albeit slower now, but I'm still happy with the way things are going so it motivates me to keep going.
Plus, I just have to look at that picture and it re-cements my resolve.