How do you keep going?

I know some of the struggles I've had in my journey to health is perseverance. I think that at times when I'm working on something difficult, I will stop when I think I have arrived. I will have all of these amazing deadlines ready and when I get to the deadline, I'm like...DONE!

For example, I was working out and eating well before the wedding. I felt really great and felt that I was gaining a lot of insight on my health. Wedding, honeymoon and back to some old habits. I may or may not have eaten a lot of our wedding cake for a week. It was pretty awesome though. But obviously not the most nutrient dense way of supplying my body with fuel.

How do you keep going in a workout? Or eating well? Or writing out menus? Measuring portions?