The idea of discovery is one that is rooted in seeking out something new. Think of those who set sail during the Age of Exploration to find new lands. They did so with a sense of excitement, enthusiasm, and hope. However, at the same time, they understood that there was anxiety present, as well as fear. Simply put, they had no idea where they were going and where they were headed. The only reality they knew is that where they were going was a risk, one that would mean that they would not see their homes for a while, if ever again. However, in pursuit of their dreams, they made this call.
In this setting, the quote helps to bring out how risk is inherent in any new adventure. The idea of undertaking new risks and challenges carries with it the foray into new and virginal territory. The comfort zone of the Status Quo is absent in such a conception. For those who wish to undertake risks and endeavors that might help to define one's place in the world, there is an understanding that doubt and insecurity, the inability to look back to the "shore," is going to be a part of this. One has to accept this risk in order to take that chance that proves to be alluring and appealing.