For me it was being sick and finding that a lot of foods made me feel crappy. Didn't know it was high blood pressure at the time, but just started eating really light - meats, veggies and fruit. Not much else for a few days, lots and lots of water and herbal tea, sometimes with Stevia (a natural sweetener that stablizes blood sugar).
Anyway just started eating less and cutting carbs and processed foods - no 'diet' snack items, but just healthy stuff. Now I can go almost all day and think 'crap, I haven't eaten yet and it's 4' then I have something healthy if I feel like it. I'm sure if someone looked at my diet they'd be horrified and say 'oh you have to eat more of this or that (grains are usually really low on my menu, not that I avoid them completely but if I'm not hungry or don't have a good option for one then I don't have it).
I have 'goal jeans' I work to fit into, wearing a pair now that were goal jeans a few months ago. Putting them on and not being able to do it right before a meal is a good motivator for me. I'm on my last pair of goal jeans now that are smaller than I remember ever wearing, not labeled as such but measuring wise (otherwise I'd never have bought them).
I did find though certain foods made me hungry shortly after I ate them, the meal replacement shakes were usually bad for that, as is cereal, grains and sugar...