Make a pledge card
A setting takes three seconds to undo. Since no software can add friction to that, a person can. Write your rule on a card, send it to someone, and going back costs a little more than it did.
The rule you type and the days you keep stay in this browser only and never reach our server. The card image is drawn on your device.
Reading this browser
Only the days you kept are shown. Days you missed are not counted anywhere, and nothing here can be broken.
With the rule written down, the phone is worth changing too. The order is device and OS specific.