Stress
We're not going to mince words here: this is a very stressful job. Not only will you undergo a great deal of stress just to get the job, but you'll be under a great deal of pressure for most of your career.
Arguably the most important aspect of your job is staying current. You'll need to be so on top of the latest news that you can predict new trends and emerging ideas. You'll also need to know what rival companies, researchers, or entertainers are up to, just in case their new products, developments, or hit singles appear to be a bit too similar to those of your clients. Rest assured, you'll always, always be working. So yes, to make a long answer long, break out that stress ball and a roll of Tums.
But, potentially frightened Shmooper, keep in mind that you'll be paid out the wazoo for being so on point. Plus, on the ultra-bright side, you'll be both highly informed and heavily entertained at all times.