I know from personal experience how hard it is to really change your lifestyle. Four and a half years ago, I weighed 250 lbs -- I'm 5'11". I was relatively active, skiing 40+ days a year, hiking, and thinking that I rode my bike a lot; about 1500 miles a season. In fact, I thought I rode enough the previous season that I'd be able to attempt Ride the Rockies, a 6 day stage ride in Colorado that's about 420 miles long.
For years, I'd been telling myself that my weight didn't really matter; that I was a "fit" fat. No doubt my activity level was higher than most. But I always deluded myself from making the lifestyle changes that were necessary to lose weight and gain real fitness.
Setting the goal of doing the Ride the Rockies was the first step. I hired a cycling coach/trainer who told me that it would be a stretch to do it even though I was starting in January for a ride in June. A month into training, the results of the lottery came back -- my buddy and I were unsuccessful in obtaining a spot. But there was a ride the week after Ride the Rockies: the Bicycle Tour of Colorado. However, instead of 420 miles, it was 520, and instead of 25k of climbing, it was 35k. A much tougher ride. My cycling coach said it would be tough, but I could do it if I did the work.
And work it was. My training schedule peaked at 16-18 hours of training a week for a total of more than 220 miles a week. I also did 2 days of strength training to build my base metabolic rate and take off weight. It was tough, but I did manage to lose 30 pounds that spring, which is pretty remarkable given the training load. I completed the BTC, although I had to SAG my way up Independence Pass due to non-conditioning issues (I got hypothermia coming off of Cottonwood Pass in a downpour and it sapped my energy).
I'm telling you this story so you hopefully take this away. For me, it never was about losing weight as an objective. That's just too abstract for me. Instead, I had to commit to a lifestyle change, and in order for me personally to do that, I had to have a big audacious goal. That goal was really audacious as I had risen a century only once before, and I never climbed; my idea of a hard climb was a 4% grade that gained 100 feet. But having that audacious goal gave me something to be accountable to. It was a feasible goal because the training schedule to get myself into shape to undertake it consisted of tasks to be accomplished every day, week, and block, meaning that the big audacious goal was complimented by a bunch of little goals. And that means I could hold myself accountable to my training schedule.
Now, 4 seasons later, I'm down to 180 lbs. I'd still like to lose 10-15 lbs. I'm taking it off slowly. Season 1 ended with my weigh around 220, Season 2 at 210, Season 3 at 200, and now I'm down to 180. If weight loss was an end to itself, I'd probably could have taken off the weight more quickly. But I see it as a consequence of my goals rather than the objective. And setting goals and objectives that interest me let's me achieve the weight reductions that have greatly improved my athleticism, health, and happiness.
Best of luck to you,