"Crossing the great stream" is a phrase that recurs often in the I Ching. Change is our only constant, and as life changes we come to intervals of transition, times that demand significant inner and/or outer change from us. The problem is that organisms tend to be conservative; they try to defend the old equilibrium, the homeostasis, the status quo, and resist change. We need to move with the cycle of change or else we are overwhelmed by it, or fall into stagnation, dithering at the edge of the great stream, imprisoned by doubt, fear, or lazy inertia. Depending on the position of this card, this is a propitious time to cross the great stream, to move with the curve of change, make the transition and discover what is on the other side.
Often it is our own inner resistance that is the toughest obstacle to overcome. Sometimes other people or forces are what most resist us making the change. Inner or outer forces may seek to defend the status quo and archetypally we call these forces "threshold guardians
The famous test pilot, Chuck Yeager was the first person to break the sound barrier flying the experimental X-1 in 1947. As he approached the sound barrier there were horrible vibrations that caused him to feel that the jet might be shaken to pieces. Then there was the loud boom as he broke the barrier, and then everything quieted down as he began cruising at the new hypersonic speed.
Summon your will to cross the great stream. As Shakespeare put it,
"There is a tide in the affairs of men, Which taken at the flood, leads on to fortune. Omitted, all the voyage of their life is bound in shallows and in miseries. On such a full sea are we now afloat. And we must take the current when it serves, or lose our ventures."