After all, "pro" is short for "professional," and there's a lot that goes into being a true professional in the tattoo industry.
You may have decided you want to learn how to tattoo because you think the work looks interesting and because you like the atmosphere in the tattoo shop. There is definitely a whole culture, or subculture, when it comes to tattooing. Much of this comes from the fact that tattooing used to be considered very subversive. Only the "bad boys" and "bad girls" got tattoos. Getting inked was a sign of rebellion, of not conforming to society's rules.
Many of the people who choose to learn how to tattoo feel like they fit in well within this culture. To be sure, that culture has been changing over the last decade or two. While many people are still not fans of tattoos, they have definitely become much more mainstream. That said, a lot of tattoo artists are still throwbacks to this earlier ideal. You will find that most of them have lots of tattoos themselves. Many have piercings, and there is definitely a bit of a "tough guy" or "tough girl" image that these folks live up to.