How does a sprag work

Something I've pondered. I know there has to be a transmission person out there who can explain this in terms the layman can understand.

From an online HOT ROD article:
"Transmission Drivetrain Breakage
Don't Let Your Sprag Sag"

"....There are many ways to cause an overrunning clutch failure, but drivetrain breakage is the most common. When a drive line component behind the transmission fails under power, the engine revs freely and so does the transmission. The overrunning clutch is designed with spring loaded rollers which help slow and stabilize the transmission's rotating assembly. Since the energy of the transmission and engine are absorbed in the overrunning clutch, and then transferred to the housing, or sprag, which is pressed into the aluminum case, the sprag will actually try to spin itself out of the transmission case, losing its pressed fit and causing irreparable damage..."

When spun by hand it will spin freely in the sprag one direction but locks up the other way. I know this sounds stupid but I'm not a transmission guy. How does it slow the transmission from free spinning? It seems to only allows free spin or none at all like a ratchet. I don't see any braking action to slow or stabilize.

Thanks. Always looking for an opportunity to learn every day.