I'll put up my bias right off: I don't have any tatoos and never will. Not that I hate them or anything, and I've seen some pretty way cool tatoos, it's just that they're not me. Besides, if I got one I expect I'd be sleeping on the couch!

As the other answers mentioned, these things are permanent. While there are methods to remove tatoos those methods aren't perfect and they take time.

Also, most of us change our world view several times during our lives. If you're in one frame of mind at 20 you'll likely be in a different one at 30 and very different at 60. But you'll still have that tatoo.

Now if you're Yakuza it'll probably be ok, but for the rest of us?

Also, consider that as you get older and your skin ages your tatoo will look different. So consider your choice carefully.

Have you considered a temporary tatoo? Admittedly, you're not going to get a piece of way cool custom art on your arm with a temp (a buddy of mine had a dragon wrapping around his shoulders,) but you might find one that's close enough and it might give you an idea of how you'll feel wearing one.

Good luck!