Viseu et al., said that the argument "has been well documented in the privacy literature as a stumbling block to the development of pragmatic privacy protection strategies, and it, too, is related to the ambiguous and symbolic nature of the term ‘privacy’ itself."[6] They explained that privacy is an abstract concept and people only become concerned with it once their privacy is gone. Furthermore, they compare a loss to privacy with people knowing that ozone depletion and global warming are negative developments, but that "the immediate gains of driving the car to work or putting on hairspray outweigh the often invisible losses of polluting the environment."