The real reason for nail-biting and other 'bad habits,' according to psychologists

In "Controlled Explosions in Mental Health," clinical psychologist Dr. Charlie Heriot-Maitland examined why people stick with bad habits that seem to work against their own best interest.

Drawing on years of clinical research and therapeutic practice, the expert reveals how the brain prioritizes predictability and safety over comfort and happiness.

For much of human history, being caught off-guard could be fatal, research shows. "The brain prefers predictable pain over unpredictable threat," Heriot-Maitland said. "It does not like surprises."

When faced with uncertainty, the brain may opt for smaller, self-sabotaging behaviors rather than risking larger, unpredictable ones.

The book argues that "the brain uses these small harms as a protective dose to prevent further harms." Procrastination, for example, may create stress and frustration, but it can also delay exposure to the higher-stakes fear of failure or judgment.

"Our brains have evolved to favor perceiving threat, even when there isn't one, in order to elicit a protective response in us," Heriot-Maitland said.

Self-criticism, avoidance and actions like nail-biting can function as attempts to manage the "dangers."

Gallagher noted that the book leans on clinical insight rather than empirical research.

"That doesn't make it wrong, but it means the claims are more interpretive than scientific," she said, noting that more data is needed to determine what is happening on a "mechanistic level."

"I encourage my patients to think about short-term pain for long-term gain, because if you just respond to discomfort and distress in the moment, you might find yourself in longer-term patterns you don't like or want," Gallagher said.

"I don't think it explains the motivations for all people, as everyone is different, but I think it can certainly apply to some."

Heriot-Maitland noted that everyone has a choice in how they handle their own potentially harmful habits.

"We don't want to fight these behaviors, but nor do we want to appease them and let them carry on controlling, dictating and sabotaging our lives," he said.

Gallagher shared the following practical tips for people who may notice these patterns.

Instead of asking yourself "Why am I like this?" try focusing on the function of the behavior, she advised. For example, does it serve to soothe, numb or distract from other fears or threats?

"Observing the behavior with curiosity helps weaken the automatic threat response," Gallagher said.

"If the brain fears uncertainty, gently introducing controlled uncertainty can help retrain it," the expert recommended.