Getting out of the "all or nothing" mindset just takes time and practice. But once it's done (from personal experience), the feeling is fantastic! I used to stuff up once and then think, "well, the day is ruined now I may aswell gorge myself" but now just after taking some time and putting thought into telling myself otherwise I feel such an accomplishment. Oh I'm just babbling and not making much sense but essentially, just put in effort (took me a number of months) and you will achieve!!