I just finished reading "Can't Hurt Me" by David Goggins. David is one of those people who pushes himself to physical limits. He explores and maximizes the potential of the human body. And most of the time while he is pushing his physical body, he is fighting against his inner "protecting" voice--the reptilian part of the brain that enabled survival and evolution all these years. It's the voice that wants to keep us safe, but is seated in the perspective of fear. This inner voice is just doing the job it knows how to do, But it is not deep in wisdom of what you can do to push yourself more. You can do more than this voice will tell you.
A few years ago I read the memoir of a woman who won the Ironman in Kona several years in a row. Up until reading her book, I assumed athletes who achieved these great and insurmountable feats had physical talent that I was not born with. What I realized, while genetics or "talent" does play a factor, it's really about the mind game. Can you keep going even when your mind tells you to stop? It requires courage, bravery and support to move beyond the inner voice that is trying to protect you. It tells you to stop or gives you many, many reasons while taking a leap of faith or chance to do more is not a good idea or you are not good enough to keep going.
In the end, everything in life is a mind game. Whether it is pushing yourself by your own choice or enduring something physically or mentally hard. It is all a form of development. In the end, we can handle more than we think we can whether "voluntary" or not. Are we not amazed and inspired by people or experience rough challenges and keep going and come out stronger? Are we not inspired by people moving beyond (or through) this inner voice dialogue telling them to stop or "you can't do this" to accomplish more than we think we can handle?
What's possible for you if you found a way past (or through) that inner voice? What would you achieve?