One thing I've noticed with people who want to make a bold change (myself included) is that they set goals for themselves that are quite lofty, and then beat themselves up if they don't hit them.
For example, you may have an aggressive rule that you will only eat 1,500 calories a day to lose weight.
Then, inevitably, one day you have an unexpected outing or event and have 1,600 calories. You chastise yourself for messing up.
Yes, you went over your target, but 100 calories one time is unlikely to make a difference in your diet. However, chastising yourself like that is more likely to make you associate hardship with the diet you have, and give you less motivation to keep going later down the road. A diet needs to be sustainable, and it's pretty hard to sustain perfection.
One way I combat over-correcting or intense feelings is to take a step back and look at the longer-term consequences. For example, if I hit my calorie target 100 days in a row and then go over by 100 calories, that is only 1 calorie per day. Inconsequential! Even more likely, other days I was under my target, and that more than made up for my minor slip-up. This is one reason I keep 7-day and 30-day averages in my food log. It helps to smooth out the highs and lows.
Really, your goal should not be perfection at all, it should be to keep going and make forward progress. That is all that matters in the long run.