In Howard C. Cutler's biopic of the Dalai Lama, The Art of Happiness, the Dalai Lama includes a chapter about the necessity of pain as expressed through the experience of lepers. One of the symptoms of leprosy is an intense numbness of the affected areas that causes a complete lack of sensation in those body parts afflicted by this disease. The Dalai Lama explained how the lepers would then become subjected to further problems due to this numbness. What kind of problems? Some of them would sleep peacefully as rats gnawed away at their flesh, further exposing them to even more tissue loss and new infections. Some of them would engage unwittingly in self-destructive acts like reaching into an open flame to grab an object because they were immune to the heat of the flames.
In Ed Miller's site notedpokerauthority.com, I had recently replied to a forum response that had quoted (forgive me if this was the second-handedly misquoted) a Stoxpoker instructor who recommended being "over-rolled" for your intended game. Even though I was able to read between the lines here, I don't like this terminology as it can be very misleading. As I had stated in my response, I strongly believe that the losses should sting (yet not be devastating) and the wins should have the ability to be satisfying. If the losses don't sting, you might find yourself reaching into that open flame far too often (i.e. stacking off too much with sub-par hands) or having rats chew away at your flesh (i.e. calling too many raises with trash hands only to fold when you fail to connect).
The sensation of pain at the loss of money is meant to protect us. You have to find your own personal pain threshold that allows you to perform optimally at your chosen stakes. These are your meaningful stakes -- and that can not be overstated. So once again, to quote myself, I prefer the term "comfortably-rolled" to "over-rolled." A minor sensation of pain creates focus, an over-sensation of pain causes fear. Stay focused, not oblivious or fearful.
And since every poker situation always has an "it depends" factor, I am now going to contradict myself. There is one situation in poker where it is appropriate to be completely oblivious to pain and that is in the early stages of a rebuy tournament. A skilled person who is ready to burn through a considerable number of buy-ins during the rebuy period is at a great advantage to the nits who are trying too hard to protect their stacks. Now that is not to say that you just shove it in with any two cards -- you are still looking for an advantage but you should be playing at stakes low enough that you are completely numb to having to buy back in as many times as necessary to capitalize on your advantage.