As the boats start to move backward in the water, the fisherman begin to ponder their predicament. The stuttering motors were the only source of propulsion for the boats, and the river is now rapidly sweeping them downstream towards a huge waterfall. They knew about the fall, but thought nothing of it while they each had plenty of gas. Now they realize, it will surely kill them.
The first fisherman considers the problem and becomes depressed. Seeing no easy escape, he broods on his impending demise. All he can think about is that final plunge over the falls. He is consumed with hopelessness and regret.
As he approaches the falls he is just sitting motionless - thinking sad thoughts.
The second fisherman considers the problem and tries to avoid depression. Seeing no easy escape, he refuses to even consider his impending demise, and instead contemplates the good things in his life. He tries to calm himself by whistling a little tune, and manages to convince himself that all is well.
As he approaches the falls he is rocking back and forth to his own music - thinking happy thoughts.
The third fisherman considers the problem and recognizes it as an exciting challenge. Seeing no easy escape, he lets his mind roam far and wide, rejecting no idea that might prove useful. He thinks, "I am a fisherman, and fishing is what I do best", and so hits upon an idea to save himself. He will cast his line into the river, and with all his angling skill, he will catch a fish big enough to pull him back upstream to safety.
As he approaches the falls he is fishing - thinking "Boy I love my job."