When I saw in the original post about 'I'll start Monday', I have absolutely been there! The key to me is remembering to start NOW. When I get off track, I don't think about starting fresh the next week, I think about starting it right then, that I can get it right immediately, that a fresh start doesn't have to be on a Monday but the minute I make a decision that I want to be better. Otherwise, I use it as an excuse to not be healthy until Monday rolls around, and usually I've already gotten off track before I realize it's Monday. I really think the key to staying motivated, as someone already posted, is to be realistic about it. Don't think about NEVER going over your calorie allowance or working out EVERY day, and don't beat yourself up if have a bad day (or two or three!), just tell yourself you know you can do better the next day, and you will :)