The main questline. When sent to visit Lagon, you can pick up a sidequest to look for a lost sailor. the sailor is in Coral pools, and when you arrive on Lagon’s isle you can see the silver ? to send you there.
A player is naturally going to be inclined to finish side quests first, so will likely go there, before heading to Moonlit Shrine. And in doing so, may very much likely ALSO collect the tablet shard, in Coral Pools, while collecting the eggs/crabmeat for the sailor.
This is a fine, speed running technique as an option for a player. however, again, its also likely going to be the average experience for every player the first time… which will cause them to skip a bit of the story.