The only mentality that brings me through a fast is “do anything it takes” (more accurately, not doing anything). Reopening the timer wishing time sped up, thinking about food, forgetting about it, remembering it, not forgetting about it, for hours, hours after that, check the timer, it’s only been 15 minutes?? etc. Then after what feels like an eternity you reach day 3 and it’s a breeze.