I've been thinking about a quote from one of the Discworld books which went something like (from memory and not in the tone of Terry):

The thing about insurmountable mountains is that they are until they aren't. And then a generation after that old ladies will stroll up to its peak as an afternoon stroll.

What I took away from it was that things are really hard until someone does it the first time, and then it gets a lot easier since there's a way.

Anyone know which book this might be from? Or what the real quote was?