Everybody has things that they do that they quickly make a habit out of -- and not all of them are very good. Things like chewing on your fingernails, procrastinating homework, being way too competitive, or even being very unobservant and tripping all the time over nothing.
Habits are formed all the time out of boredom, or nervousness, or to think, or just for plain fun. High school students around the Top of Utah admit to a variety of bad habits.
Personally, I chew my fingernails. I am always being told to stop, but that is only when I'm forced.