Do you feel deprived?  If you are like most people who are on crash diets, you feel deprived and what happens, right on schedule, you sabotage your diet.  The reason why diets fail, in addition to you feeling powerless to control your lifestyle, is because diets are so restrictive.  You might lose weight and then you gain it right back because you felt deprived for so long.  Then you want to reward yourself.  So, avoid feeling deprived by eating smaller amounts of what you want as opposed to huge amounts of everything.  Then when you do, you feel much less deprived and much more in control.  The idea is to change your lifestyle on a permanent basis, so eat in little bits as opposed to huge amounts at which point you will avoid feeling deprived.