Originally Posted by
oldbobcat
. . . The chainring pushes the chain toward the tension pulley on the rear derailleur. . . .
Pedaling in small to small, with an excessively long chain, the chain sags toward the ground. Not much pushing going on.
Remove a connector link from a chain and turn the cranks (preferably by hand, with the bike on a repair stand), and the chain drops straight down to the floor off the front of the chainring.