Fiver is a small and weak rabbit, mostly dependent on his older brother Hazel, and prone to fits of clairvoyance where he can predict some future events. As the book progresses, it becomes clear that while Fiver is timid, he possesses a certain inner strength, and he is willing to be a laughingstock for his predictions as long as the other rabbits take notice.
"Do you think we can risk it, Fiver?" he asked.
"I can't see why you're bothered," answered Fiver. "You went into the farmyard and the shed where the hutch rabbits were. This is much less dangerous. Come on
-- they're all watching while we hesitate."
Fiver hopped out on the road. He looked round for a moment and then made his way to the nearer end of the bridge.
(Adams, Watership Down, Google Books)
This example shows how Fiver is willing to trust his instincts over his fears; while the other rabbits are scared of the bridge, not fully understanding how it functions, Fiver knows that they need to cross to survive, and that the longer they hesitate, the more danger they are in. In addition, he has no premonitions about the bridge being dangerous, and so he knows that they can cross it safely as long as they hurry. Without Fiver's assured nature here -- unusual for him -- the other rabbits would spend too much time talking and debating the issue, and be in danger both from cars and hawks, one of which they see while crossing.