Jerome cursed under his breath as he stalked further into the forest.
"Small-minded fools!"
He heard the sharp sound of a branch snapping behind him and whirled to face his pursuer, bracing one foot behind him in a secure stance. That he saw no one mattered little, as the ferns he had been pushing through had been hiding a ravine!
His rear foot slid rapidly on a scree of mud, small stones, and rotting leaves. His shock was quickly eclipsed by the insult to the powerful muscles of his thighs as they tried to keep him upright at the gap's lip. With a small scream he curled up and fell to his side, his downward motion unchecked.
A sapling spun him wildly when his neck struck it; the pain shocked him into panicked motion. He scrabbled wildly at the rocky slope, to no avail. His efforts cost him several fingernails and his attempts ceased as rapidly as they began.
He rolled painful down the steep slope; he screamed again as a protruding rock dug painfully into his back, causing him to briefly arch backward, until further minor assaults caused him to once again curl into a ball. With a last despairing wail, Jerome flies into space as the steep slope beneath him becomes a shear wall.
He lets out one last piercing shriek as he lands on his right hip and the pain causes him to momentarily black out. He awakens shortly in agony, bruised and bleeding, shaking from the overload of adrenaline in his system, speechless. Shortly he recovers enough to pull himself to the minor shelter offered by an overhang at the base of the ravine, a few feet high and deep. He continues to shiver convulsively, staring at nothing, until a healing sleep overtakes him.
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Otiluke walks forward, sword in his right hand and shield strapped to his left forearm. Behind him, Bigsby holds his torch high; Otiluke's shadow dances before him, describing odd shapes and forms, distracting him from the task of keeping a careful watch for whatever creatures may lurk in this dank hole.
His reflex causes him to pulls his arms in and crouch down in surprise, thus the first creature lands solidly on his shield, its claws scrabbling at the hardened leather covering his shoulders. Otiluke* throws it off and assumes a more aggressive stance, at an angle so as to be fully behind his shield with his right arm up to threaten over the shield with his sword.
There are three of the creatures; the one he threw to the ground regains its balance as a second attacks him and the third attempts to rush past him to attack his less heavily armored companions. He quickly lashes out to check the third's advance, then strikes the second with his bulk, pushing it back.
Otiluke sees a flash from the corner of his eye as Bigsby lashes out and feels a puff of wind as Tenser sends an arrow into one of the snarling homunculi before him. The creature squeals and pulls the arrow from its rags with its jaws. The arrowhead sheds a drop of blood before the creature snaps the shaft and leaps forward again.
He strikes out to his left with his sword and quickly balances the awkward motion be lashing out to the right with his metal clad foot. He feels both blows land and one of his foes staggers back, squealing. Otiluke then lets out a brief yell as a javelin slams into his exposed torso. It fails to penetrate his hardened leather shell, but several ribs complain and he staggers, gasping in pain as several sensitive organs register the shock.
The screeching demon to his right, favoring its leg and scorched on its face launches itself at Bigsby, only to collapse to the ground as a glowing orb strikes it in the head. Shards of light fly past Otiluke and shred the squealing creature he so recently shoved backwards. Meanwhile, Tenser launches an arrow into the throat of the demon he had so recently annoyed.
Gasping slightly, Otiluke jogs forward for the creature that struck him with the javelin, only to have another land in his shield. He lets out another grunt of agony as his left shoulder is cruelly wrenched and he turns slightly to the side. The creature flies out of the darkness, dagger in hand and plants it in the exposed flesh of Otiluke's upper arm.
He staggers backward briefly, howling, then steps forward and slams his sword into the creature's side. Bone crunches under the layers of rags it wears and he flings it into the wall, where it slumps unmoving
Otiluke leans his arm against the wall and presses his face into his forearm, sobbing in rage.
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I'm just trying to imagine a few scenarios. In the first, some guy fails a reflex dojigger, then fails a few more as he falls. He receives some minor injuries while sliding (such that if he'd manage to catch himself before the big fall, he wouldn't have escaped unscathed), then sustains a major blow when he freefalls to the ground. He ends up below 0, but stabilizes, regains consciousness, and crawls away to use up all his healing surges.
In the second, you've got a dwarven fighter in the lead with a controller and a striker behind him. He's the only one able to act in surprise, uses a free action to stop a kobold attempting to move past him, then uses some sort of per-diem thing that lets him do two things at once (I'm really fudging, here). The controller and striker take care of eliminate the melee slitches. So he charges at the skirmisher and gets hit. Then he uses a "when bloodied feat" to get a bonus and the scenario ends.
Even though Jerome (the faller) never suffers a serious injury until the end, the sum total is enough to shock him and leave him open to attack. The final one leaves him unconscious and completely helpless. Would it have done so without the previous injuries? If Jerome's player had failed to stabilize him, maybe it would have meant that at some point one of his injuries opened a serious internal bleed that simply wasn't obvious. But he made his save, so it looks like that didn't happen.
Likewise, Otiluke was still able to fight, but at the same time he'd been hit pretty hard. The first kobold landed on his shield and scrabbled, right? So it didn't hurt him, it still tired and distracted him, and he's lucky he landed that AoO that stopped the kobold trying to rush past him. The he used a Tide of Iron to keep the other two clear. But then he was weakened further while attacking. He's obviously still able to attack and move, but his ability to defend himself is going to be hampered. Then he's got another serious wound that keeps him from using his sword effectively, then another that hampers his shield. Even though a cut on the arm isn't life-threatening, the next blow (that never happened) might just have gotten through and hit him in the neck!
Instead, Otiluke gets his arm bandaged and carefully applies a hot compress to his shoulder to keep it from stiffening. The next day he's almost as good as new. And if he doesn't get to rest? Then he's low on surges, weak, and open to "serious" injury.
Suffice it to say that you don't have to get seriously hurt for a hurt to leave you open to a serious hurt. Don't think of HP as a collection of wounds. Think of it as a collection of minor injuries that, together, leave you open for the one that kills you.
* I know Otiluke was a magician, hence his Resilient Sphere, but

.