In all those nature documentaries, when they show the wolves chasing down caribou, or when they show any predator while hunting (lions, hyenas, great white sharks, etc.) what they don't show you is just how dangerous it is for the hunter.
When wolves go after caribou, elk, or deer, it's never a sure thing. Least of their worries is the animal getting away. They can always try again. Their biggest worry is getting injured by the prey. All it takes is one flick of a head with antlers, and the wolf will be seriously injured. One kick can break the wolf's ribs. This will make hunting extremely difficult and the wolf may even die.
The same goes for all predators. Nature has bestowed prey animals with a multitude of defenses which can be dangerous to predators. Rabbits have speed and powerful legs (have you ever tried holding a pet rabbit for too long?) The ungulates such as deer, gazelle, antelope, zebras, and so on, all have powerful legs. One kick can do much damage to a predator. Even sharks are sometimes found with scars from the defenses of giant squid and seals. The hagfish emits a sticky slime than can choke an animal that tries to eat it. And of course, many animals (and plants) make themselves poisonous.
There's no sure thing in nature. A predator might have bigger teeth and a loud roar, but cornered animals often have something up their sleeve. They can make even a lion wish it had just continued sleeping in the shade.
For a human analogy, consider the arrogance of powerful armies, and what happens when they underestimate their opponents, who have less guns, no missiles, no tanks, and no fighter jets. Be assured - they can still win! Just consider the U.S. invasion of Vietnam, or the Soviet invasion of Afghanistan. Guerrilla fighters, like prey animals, use surprise as defense. (The difference, of course, is that predator species have a biological imperative to hunt, whereas wars among humans is purely cultural.)
Just when the lion thinks he's got a meal of that gazelle - BAM! - a kick to the face changes everything.
There are some valuable lessons for self-defense: Use surprise. Attack weakness. Use what nature's given you. Don't be intimidated. Never give up.