Originally Posted by
DannoXYZ
It does guide it because the RD determines the angle the chain makes as it encounters the chainring on the bottom. The greater the angle away from 0-degrees, the more likely the chain will walk off the chainring.
Sure, the angle is less than with the rear-cogs, but RD doesn't have to sweep across 10 chainrings just to pull it off one.
This is quite true. Maybe the OP should check the rear derailleur high limit screw and consider the RD hanger alignment.