It is achievable, DH has been trying to lose weight, and has had a competition with the guys at work, with forfeits for the loser each week. (the one who loses the most weight, gets to shoot the one who loses the least with a paintball gun ;) )
The competition makes them all more determined to keep losing and not have any 'bad' days.
DH has cut down his portion sizes, he went on the 'chemical diet' for the first week to get him going, it's very restrictive, and you can only do it for a week.
After that he hasn't been on a 'diet' as such, but is following paleo rules, which is essentially only eating things that cavemen would have eaten, meats, veg and fruit. No pasta, no bread etc.
He has stopped all snacking.
He also goes to the gym for an hour and a half each weekday morning before work, and we go kickboxing once a week.
He has lost just over a stone each month.
He hasn't stopped treating himself all together though, on Fridays after the weigh in, they all have a meal/snack they 'shouldn't' and at the end of each month we have had a take out to celebrate him winning 'man of the month' (which means he has lost the most weight overall in the month)