Image: Sucker Punch Productions / PlayStationOfficial screenshot from Sucker Punch Productions / PlayStation.
Common Courtesy is the Iki Island trophy for finishing the unwritten tales. These short tasks are not on the map or in the journal, so you have to stumble on them.
Talk to people you meet on Iki and help them. Finish Bury Ship Captain, Hachibee the Beekeeper, Helping Kodama, Saving Peasants From Lake, the Raider Memorial Archery Challenge and Retelling Legends to Uta.
The Collections menu shows which ones are still missing.