What is this moment of crisis? I wanted to explain it like so: In general we refer to the Yetzer Hara, or the animal soul, as something evil. In reality, the Yetzer Hara most of the time plays a role more like training wheels. It makes you seek out the right things for the wrong reasons. A person can live their whole lives listening to the Yetzer Hara and accomplishing mainly good. He can make a good living, marry a nice woman and have a beautiful family. These are all things the Yetzer Hara encourages.
Sometimes, though, the Yetzer Hara encourages us to go beyond our own personal boundaries and cross into areas that are more black than gray. These are the times of nisayon, of challenge, of crisis. These are times when suddenly all of the good intentions and baby steps you made toward holiness come back to pull you across the finish line. This is the time of crisis about which Rebbe Nachman was speaking.