Where do bad driving habits come from?

I don’t have a good answer for this question but I do wonder where bad driving habits come from.  I was compelled to think about this after I was almost impelled over the side of the remarkably high bridge connecting IH10 and Loop 410 on Sunday morning by an oblivious young woman concentrating on texting, who may not even have noticed what happened. 

I suspect such insanity creeps up on you.  You try something once in a relatively safe environment and then the foolishness takes on a life of its own.  I dare say I am not a paragon of virtue, either.  Anyhoo, what kind of witless driving are you seeing and what do you think is going through the minds of the perpetrators?