When we push our limits - when we go beyond our current boundaries - we are exploring the unknown.
If I go just one mile farther this time, how will my body react? What will I see if I climb just a little higher? If I spend one more hour on this project, what might I accomplish? Can I do this repair myself?
There's only one way to know for sure.
Most of the time, there's no real penalty for trying. In the best case, we discover that we are capable of a little more than we thought we were, and our boundaries are redefined. The worst that will usually happen is that we fail, and in so doing, we learn that the boundary we've been operating at is real (and we've been kicking butt this whole time).
Both scenarios create opportunities to set new goals. Boundaries and limits are temporary, and the Unknown is just a chance to find out.
A couple of weeks ago I was proud to have broken the 17-mile mark on my weekend run. Today I found out what 18.5 feels like. It hurts, but soon I will do more.