I gave a presentation this morning on the chapter I wrote in the book Power to Change - 5 Ps to making life-enhancing changes. A big part of what I focused on though was the idea (that I find very intriguing), that your comfort zone is in fact the least safe place to life. 
I discussed how the universe and your soul are always guiding you and working behind the scenes to help you grow and evolve and to eventually find fulfillment by living out your life purpose. I used the first P - Pain Point to talk about the notion that sometimes you may need a whisper from your soul to get you moving. Other times you may need a nudge and, on occasion, you need a real painful push. Pain is one way sure way of getting your attention and encouraging you to make changes.
I also shared an example from my own experience when I lost my job while I was three months pregnant. In that situation, I was ejected from the comfort zone of my full-time marketing position into contract work. In retrospect, the contract work has, over the years, allowed me to spend more time with my family, pursue my passions and find my life purpose. So all I can say now is - thanks for the push!
If you believe that pain is one way of getting you to take a risk or try something new and different and expand your potential then is follows that if you stay too long in your comfort zone, ignoring whispers and your sense of 'knowing' that something needs to change and the little nudges etc. then your comfort zone becomes a potential 'pain' zone - thus an 'unsafe' place to live!
If you do want to make changes though, your fears and concerns do need to be addressed to make the change feel as safe as possible - thus expanding your comfort zone to help you reach your potential without destabilizing you and upsetting your ego.
Food for thought - I always love to hear your comments!
Jackie