With each passing year, the marketing world faces as many new challenges as it does opportunities. The continued proliferation of digital media is bound to make marketers' jobs easier in some respects, but it also presents significant risks -- both to individuals in their everyday jobs and to the larger industry as a whole. With all the potential data points that can now be measured, perhaps one of the most important challenges to the marketing industry is learning to recognize which metrics are most important, as well how much is still unknowable. Otherwise, there is the risk of moving backwards. To get a better sense of the unique challenges faced by individual marketers on the ground, we went straight to the source. Here are the top challenges that real marketing professionals shared with us.