It's not that you forgot. You knew you had to leave. But somehow "I'll start getting ready in a minute" turned into 30 minutes of doing something else entirely. Your brain doesn't feel the deadline until it's already past. Backward planning makes the start time concrete.
You know the appointment is at 2:00. You know it takes 20 minutes to drive there. But the chain of steps before driving (find keys, change clothes, use the bathroom, grab your wallet) doesn't register as time. It feels instant until you're doing it. That's time blindness: you can read a clock and still not feel the deadline approaching.
Ready Time sends you a notification when it's time to start getting ready, not when it's time to leave. That's the difference. The app works backward from your leave-by time and tells you when the first step starts. You don't have to hold the whole sequence in your head. Just follow the next notification.