Comfortable is good. And comfortable is nice. Shoes should be comfortable. And so should pants, your sofa and your pillow. But if you live your life in a bubble of comfort, you'll become stagnant.
I was once told that, "if it's not uncomfortable then you're not making a change." That statement couldn't be more true. Take for example, the long run. When you first start running, a mile might seem like an eternity, but over time you add distance, pushing past the point of comfort (what you know) and before you know it three miles is short and six miles is "kind of a good workout." Your mind and body have adapted to the stresses placed upon them and you have evolved. You are changed. Stronger. Better.
Change is never made by standing still and staying in your comfort zone. And making a change is never easy. If it were, we would all be successful in every aspect of life. I truly believe that ANYONE can make ANYTHING happen with enough hard work and determination. But, I also believe that EVERYONE is stopped by self-imposed limits. We all have our "thing" that we just can't do. Or won't do. Or don't want to do. (For me, it's cutting out sweets, it's a nice thought, but I don't want it enough to put in the effort.)
At the end of the day, the only thing that stops us is ourselves. Don't let yourself get in the way of your successes. Push your limits, until they fall ...