Once you have a small bubble - and the wind hits it - the glue pulls away. what is today a minor irriataion - tomorrow is a major sag.
That's the point.
I had a small bubble of around 20 cm dia. near the rear window for >2years.
One day I drove the car with all 4 windows open, I suddenly had a Pagoga headliner, it had dropped from front to rear.