The challenge with losing weight isn't just discipline, but survival, depending on your situation. The average American consumes 3,700+ calories a day. To cut that under 2,000 and lose weight, you are losing energy, focus, can become irritable, etc. It's pretty miserable. Especially when you ARE a big guy and you need that energy.
The better thing to do is taper down your caloric intake. Measure what you tend to eat by calories. Be honest about it. And then scale down slowly. Maybe shave an average of 250 calories (daily) for week 1, and if you're feeling ok, chop another 250 off the next week... etc.
If you're exercising, it's even more important to taper your caloric intake.
Anyway, that's been my issue. I'm not patient. So I always bite off more than I can chew when I start a diet, am completely miserable and unproductive, and then slip up. Throw my arms up, and say, I can't do it. Now that I finally am understanding the value and importance of moderation and discipline, I'm starting to make progress by just cutting out little things here and there and taking it slowly/one day at a time.
But trust me when I tell you, for certain people, losing weight isn't even close to easy.