As a parent, I obviously care deeply about the welfare of my children. I do not want them to get hurt, and it bothers me greatly to see them in any kind of pain. I try to keep them out of harm's way in order to avoid such things.
However, I also realize that pain is a necessary part of life, and that it teaches and informs us. To withhold it entirely from my children would be to deprive them of important lessons. Now, this doesn't mean I pull out whips and chains and beat the kids to teach them or anything nearly so psychotic. No, I don't advocate inflicting pain on children. But I do advocate letting them experience it as a result of their actions. I do advocate allowing them to enter into situations where they might be mildly hurt, situations involving some level of risk or failure, in order to teach them how to deal with pain and failure.
This is an opinion I hold that seems to be at odds with many (maybe most) parents I have met. I let my kids ride their scooters without protective gear, for instance, which some parents would say is irresponsible. However, my kids have learned how to be a lot more careful and mindful of their actions while riding their scooters than I think they otherwise might have been. My older son, who was quite reckless and willing to charge head first into walls as a toddler, now has a pretty good understanding that if he does things like that, it will hurt.
Maybe you're reading this and thinking, well of course pain teaches lessons, but a parent's role is to make sure his child is safe until the child is able to do so for himself. To a degree, this is true, but I believe a more important role for a parent is to teach his child to reach that level. It must be a balance. You can't stick your kid in the wilderness and tell him to fend for himself without guiding him and training him first. But you also can't expect him to learn how to fend for himself if you keep him tucked away in safety.
It is difficult, as a parent, to let your child walk into a situation that you know is dangerous, but I believe that just as a parent must be aware of when the risk is too great for the child, he must also know when the risk is work taking. Far too often, parents err on the side of caution. That is the better side to err on, but it is still an error, and we should work to correct our errors.