What are your true limits?

I recently was fortunate to spend some time with my friend who is 100 years old...almost 101.  He insisted I take his book home entitled, Inside Seal Team Six by Don Mann.  Since my friend was a Frogman in WWII, I wasn't going to argue with him more than I already had.    I figure I will call him and share with him some of the things I am learning from this book.

One of my favorite quotes so far by Don Mann is, "Because I figure if you never push beyond what you think your true limits are, you will never know your true abilities."  He insists that most people have no idea what their true limits are.