Black & White. All or Nothing. Nothing less than Perfection. This is how my brain works, but it is not good for me. It is BAD, BAD, BAD! The more I strive for perfection, the worse I feel about myself because I always fall short. I know that no one is perfect and yet I cannot get my brain to cooperate. I am so hard on myself that I subconsciously give up.
Striving for progress is definitely the way to go. Be proud of what you have done no matter what. When it comes to fitness, something is better than nothing. The more proud of yourself you are then the more likely you will be to repeat that action. You will want to keep going which means more weight loss and high self-esteem.
This statement is useful in all aspects of life not just fitness. Everyone makes goals for themselves in some sort of way. Take New Year's resolutions as an example. 80% of people who set resolutions never follow through. I speculate that there is a lot of giving up due to being frustrated with themselves.
Focus on your progress. You are going to mess up so just accept that now and pick your goal back up the next day and keep progressing!