I removed the login screen

Today I started a workout app: a phone app plus a server side that builds the training plan. The first version had the usual order — you open the app, you sign up, then you train. I used it myself for a day and realised the order was wrong. Here is why: this app is for one person, tracking their own workouts. Standing in a gym, opening your phone and typing a password is something nobody enjoys. And signing up gives nothing back, because the data lives on that phone anyway. So I removed the login screen completely. On first launch the app creates an account for the device itself and works with that. The user never notices — they open it and start training immediately. That same day I fixed something else. When the server did not respond, the app said "An error occurred". That sentence says nothing: is there no internet, is the server down, or did I make a mistake in the code? Now the app shows the real reason. At the end of the day I hit another problem. The program counted the training plan from the day the user signed up. So for someone starting on a Tuesday, "day one" was Tuesday. But people live by weeks — Monday, Wednesday, Friday. I tied the plan to real weekdays instead. The lesson: you cannot build an app right if you do not use it yourself.