Once you realize life is short and you should spend less time worrying about your job and more time doing the things that make you happy, such as seeing friends and family, experiencing new things, traveling, befriending people that are radically different than you, hearing other peoples opinions, etc.
Once you live life with that mentality, it's easier to see something or have a tattoo idea and go "Why not? I'll get that, that looks really really cool". And if it's under clothes and you can show it off at the beach or in bed in a non professional environment, then why not?