I am giving away lifetime licenses to my Unbroken: 75 Day Hard Challenge app to users of this subreddit. [Method]
I've run 75 Hard a couple of times myself, and the thing that kept breaking my streak wasn't the workouts or the water. It was losing track of which day I was actually on after a chaotic week, or forgetting to log a task and not realizing until it was too late to fix.
So I built Unbroken, a dedicated 75 Hard tracker: daily checklist for all the rules, a photo log so you can actually see your progress over the 75 days, and a clear view of your current streak so there's no ambiguity about where you stand. And also do it together with a friend or accountability partner.
If you're currently doing the challenge (or about to start), you can grab Pro for free — go to unbroken75.com/code, sign in with the same account you use in the app, and enter the code 75HARD.
Good luck out there. Day 1 is always the easiest one to skip, so this is your reminder not to.