Out of battery.
If your phone runs out of battery, you won't expect it to charge itself on its own. You plug it into an external source of energy to make it work again.
Our motivation, persistence and discipline also run out of battery every now and then. Just like the phone.
It's not a crisis. It's a sign that we need a trusted external source of energy that we can plug ourselves in. Sometimes, that would look like a community, sometimes a coach or a therapist, and sometimes it would be book or maybe even a song.
It's a good idea to keep such things handy because it's challenging to find a charger when the phone is almost out of battery.