I have to think that nail biting is partially genetic. My grandmother bit her nails all of her long life, finally to have fingernails in her coffin after a fairly long illness, and I have, like her, bitten my nails all my life and still doing so at 84. And yes, I believe the other reason given in this article are also true. And NONE of the products made to stop nail biting has worked for me.
Its a terrible habit, and extremely difficult to break and oh yes,...Being hypnotized was a joke! A way-around...keep your hands out of sight and be a really likable person! Good luck!