The way general average was explained to me when I took a class in it along time ago was this:
Imagine 200+ years ago. You and say 20 other principals have decided to ship a a variety of cargoes by sea. Let’s pretend we’re shipping stuff from Europe to the Americas. It’s a big variety of cargo, some in barrels, some in crates and boxes, all break bulk stuff. During the voyage the ship starts taking on water and the crew has to jettison a bunch of cargo in order to maintain stability, or fix the leak or whatever. Maybe only one individual cargo owner lost their shipment, but that sacrifice saved the entire venture. Therefore rather then that one cargo owner having to bear the loss, all the cargo owners have to equally distribute the loss.
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There are a few main types of insurance.
Protection and Indemnity
Hull and Machinery
And Cargo.
From there we must realize that each might correspond to a different person. The Ship Owner, the Ship Operator and the Cargo Owner(s) might all be different people with different concerns.