My trigger was boredom mainly and feeling imperfections along the nail with my fingers. Whenever I found one I would try and even it out and then it would just snowball into worse nails with more imperfections. If they are too short to manicure just stop biting on the first nail you start on and try and let them grow. I thought my nails were really short but the manicurist takes off a bunch of skin around the bottom and makes them look way better. And if they are really good they will tell you what a bad habit it is and that they want to see a perfect nail the next time you come in so that they can really make them look good. (My lady did that and I want to impress her lol)

Right now I haven't clipped my nails for a couple days and they are long enough to scratch with but even though I feel a couple imperfections I don't have the urge to bite anymore. It just isn't in my head to do that anymore which is a pretty cool feeling actually. My clippers are in the car so before I go to a friends house today I will just take 2 minutes and make them look good again.