That one simple phrase has been one of my personal philosophies and drivers for achievement since I was young. When facing difficulty, I find it useful to remember that any worthwhile task -- love, a business opportunity, writing meaningful software -- is difficult and complex. That's how the real world is, and the things worth working for are hard to solve and demand perseverance.
I recently heard a colleague say, "If we're not having problems, that's a problem." I totally agree.