Carryover cooking and resting happen during the same few minutes off the heat, which is why people talk about them as one move. They're not. Carryover cooking is heat still traveling through the meat after you've taken it out of the pan or oven — the internal temperature keeps rising on its own. Resting is a separate process: the muscle fibers easing back from their tightest, most-contracted state and letting the juice they squeezed toward the center spread out again.
Why the internal temperature keeps climbing after the heat is off
Meat cooks from the outside in. By the time the center hits your target temperature, the outer inch or two is sitting well above it — that's the whole reason the outside browns while the middle stays pink. That heat doesn't vanish the moment you pull the pan off the burner. It keeps conducting inward, from the hot exterior toward the cooler center, until the whole piece equalizes. The center goes on rising for several minutes after it left the heat.
How much it rises depends on the size of the gradient you built while cooking. A steak seared hard and fast has a thin band of overheated exterior, so carryover might add a degree or two. A whole prime rib roasted slowly has a much deeper reservoir of superheated meat just under the crust, and that reservoir can push the center up another 5 to 10°F (3 to 6°C) after it comes out of the oven. Pull it at your target temperature and you'll overshoot by dinner.
Why resting is a separate mechanism
Resting has nothing to do with residual heat. It's about what happens to water inside the muscle. Heat denatures the proteins in muscle fiber, and denatured fibers contract — they squeeze, wringing moisture out of themselves and pushing it toward the center of the cut under real pressure. Slice into meat straight off the heat and you're cutting into fibers still clenched tight, so that pressurized juice runs straight out onto the board.
Given a few minutes off heat, the fibers relax slightly as the meat cools, and the pressure eases. The moisture that got pushed toward the center has time to redistribute through the cut instead of sitting there under pressure, waiting for a knife to release it. Less runs out when you finally slice it. None of this depends on whether the internal temperature is still climbing. It's a texture change, not a temperature one.
Where the two overlap, and where they don't
They share a clock but not a cause, which is why the advice for one doesn't automatically apply to the other. Pull a roast early to account for carryover and you're managing temperature. Rest it afterward and you're managing texture — two different jobs that happen to use the same five or ten minutes.
That's also why a seared steak still needs a short rest even though it barely carries over. A steak's thin cross-section means there's almost no stored heat to conduct inward, so the internal temperature is close to done the moment it leaves the pan. But its fibers clenched just as hard as a roast's did, so it still needs those few minutes for the juice to settle before you cut it. Carryover cooking might be negligible on a steak. Resting isn't.