When you are trying to lose weight, you will likely start with a lot of good intentions.

For a short while you'll be right into it and it will be easy to follow your plan.

But then something happens to cause you to not follow your plan. A friend gets married, and you drink a lot of calories in champaigne to celebrate the event. You have a business lunch with a client and eating just salad doesn't seem appropriate. You have a deadline to submit a report by, and sit at your computer all day to finish it, missing your daily exercise. Whatever.

It's not the end of the world. Just realize that there are going to be days that everything doesn't go as you intended with your diet. Whatever you do, don't be hard on yourself! Tell yourself that so far you have done very well. That it seemed necessary at the time to not follow your plan, but that now theat situation is over you are going to go back and continue on with what you had planned for yourself.

It didn't happen that you got overweight overnight. And realistically it's not going to happen that you get slim overnight either.
Do your best, and if you slip a little, well, it's just going to add an extra day or so on to the time until you reach the weight you wish to be at.