I've got a few.
My first one was when I was 20. I was in University. I'd gone through a pretty low patch. I was in bad debt, depressed and stressed. I did a favour for this bloke who ran a local Tattoo shop. He returned the favour by giving me the tattoo.
To be fair: it is a rubbish tattoo. Crap Tribal design, badly done. It is, however, one of my favorites. It reminds me how far down I've been and how far I've come since then. I think in life, you can sometimes forget the crap stuff you've been through. This tattoo reminds me that things have been worse and that i've overcome them before, so I can do it again.
As for the pain aspect: I'd say the sunburn analogy is pretty close. I find that it stings a bit for the first few mins then your endorphins kick in and it doesn't really bother you any more.