One private pattern
Most people have never heard someone openly describe a lifelong habit of chewing on their tongue. Many people who do it hide it. Some do not even have a name for it. Some believe they are the only one.
For the person living inside it, the chewing may not feel like an occasional nervous habit. It can become a private, automatic pattern that runs through work, rest, concentration, stress, and ordinary daily life.
Stress could turn the volume up. But stress was not the whole cause. The loop was already there.