I started 2 years ago weighing 22stone exactly. I made myself a spreadsheet up with LOADS of different goals - 5% of my body weight, half stones, BMI ranges, big chunks (25lb 50lb 75lb etc) and it worked a treat, I always had a small goal to aim for.
BUT when I got to 5 and a 1/2 stone off I told people I was half way there and it all went wrong, I think because I just couldn't cope with having such a distant target. I've wobbled for the last year, I got half a stone more off and since then have gained 2! I'm now at a 4 1/2 stone loss with no real end target in mind and have gone back to looking at the next little success - at the moment the next one is to regain my 5stone award. Hope that made sense!