I think the beginning... the VERY VERY beginning (not the beginning this time, or last time, but the FIRST beginning) is the hardest, certinally.
At the very first beginning... you have SO MUCH to learn! I can not believe how much I had to learn in the first two years and where I am today. You have to learn which 'diet' is for you, what calories are, what type of weight loss to expect (when I started, I thought a pound a day was the acceptable rate

), you have to learn that eating 300 calories a day is NOT GOOD (again, I made this mistake too

), if you want to eat healthy, you need to figure what that is too! (I've almost got a hang of that one.) And then you have to use what you've learned on your own to go back and decide if certain pieces of common information are fact or fiction (1200 calories a day for women, starvation mode, eat more to lose weight).
I don't know how difficult maintenance is (unfortunately for me

) but I can't imagine it's harder than going into battle the very first time without any weapons at your disposal. (At least I hope it's not!!!)