Well there are a few places that I've waundered around in that would definately not be considered safe, however my guess is that isn't what he was talking about.
My bet goes with, if you are absolutely comfortable or certain with how your image is going to turn out because you've essentially taken the same image a hundred times, then you are playing it safe. There are many ways to test the boundries. I'd say to pick one that might be of interest and that is going to require you to learn something new. If all your photos have been still lifes of oranges, switching to apples isn't going be it. Try an unfamilair process, camera format, subject matter, compostition, etc. Have it be something that challenges you.